Rocks, Minerals and Fossil Fuels

Minerals in Earth's Crust

Minerals – The Building Blocks of Crust

The ingredients used to make the Earth’s crust are complex. The basic ingredients are known as elements. There are 90 known elements that exist in the Earth’s crust. These elements combine with one another in a number of natural ways, creating molecules known as minerals. There are around 3,700 known minerals found in the Earth’s crust, with dozens of new minerals being discovered each and ever year. These minerals combine to form crystals in regular and distinct patterns. Sometimes the crystals are obvious to the un-aided eye. In other instances, it is necessary to use a microscope to observe the crystals.

The physical characteristics of minerals include traits which are used to identify and describe mineral species. These traits include color, streak,luster, density, hardness, cleavage, fracture, tenacity, and crystal habit.

Certain wavelengths of light are reflected by the atoms of a mineral's crystal lattice while others are absorbed. Those wavelengths of light which are reflected are perceived by the viewer to possess the property of color. Some minerals derive their color from the presence of a particular element within the crystal lattice. The presence of such an element can determine which wavelengths of light are reflected and which are absorbed. This type of coloration in minerals is termed idiochromatism; different samples of an idiochromatic mineral species will all display the same color. Other minerals are colored by the presence of certain elements in mixture. Different samples of such a species may exhibit a range of similar colors. Still other mineral species may usually be colorless, but may display several different and startling colors when trace amounts of impurities, or elements which are not an integral part of the crystalline lattice, are present. Coloration which is caused by the presence of an element foreign to the crystal lattice, whether in mixture or in trace amounts, is termed allochromatism. Certain elements are strong pigmenting agents and may lend vivid colors to specimens when they are present, whether as a part of the crystal lattice, in mixture, or as an impurity. These elements are termed the chromophores.

Streak is the color which a mineral displays when it has been ground to a fine powder. Trace amounts of impurities do not tend to affect the streak of a mineral, so this characteristic is usually more predictable than color. Two different specimens of the same species may be expected to possess the same streak, whereas they may display different colors.
Minerals are either opaque or transparent. A thin section of an opaque mineral such as a metal will not transmit light, whereas a thin section of a transparent mineral will. Typically those minerals which possess metallic bonding are opaque whereas those where ionic bonding is prevalent are transparent. Relative differences in opacity and transparency are described as luster. The characteristic of luster provides a qualitative measure of the amount and quality of light which is reflected from a mineral's exterior surfaces. Luster thus describes how much the mineral surface 'sparkles'.

The property of density is defined as mass per unit volume. Certain trends exist with respect to density which may sometimes aid in mineral identification. Native elements are relatively dense. Minerals whose chemical composition contains heavy metals, or atoms possessing an atomic number greater than iron (Fe, atomic number 26), are relatively dense. Species which form at high pressures deep within the earth's crust are in general more dense than minerals which form at lower pressures and shallower depths. Dark-colored minerals are typically fairly dense whereas light-colored ones tend to be less dense.

Hardness is defined as the level of difficulty with which a smooth surface of a mineral specimen may be scratched. Hardness has historically been measured according to the Mohs scale. Mohs' method relies upon a scratch test to relate the hardness of a mineral specimen to the hardness of one of a set of reference minerals. Hardness may also be measured according to the more quantitative but less accessible diamond indentation method.

Cleavage refers to the splitting of a crystal along a smooth plane. A cleavage plane is a plane of structural weakness along which a mineral is likely to split. The quality of a mineral's cleavage refers both to the ease with which the mineral cleaves and to the character of the exposed surface. Not every mineral exhibits cleavage.

Fracture takes place when a mineral sample is split in a direction which does not serve as a plane of perfect or distinct cleavage. A mineral fractures when it is broken or crushed. Fracture does not result in the emergence of clearly demarcated planar surfaces; minerals may fracture in any possible direction.

The characteristic of tenacity describes the physical behavior of a mineral under stress or deformation. Most minerals are brittle; metals, in contrast, are malleable, ductile, and sectile.

The term crystal habit describes the favored growth pattern of the crystals of a mineral species. The crystals of particular mineral species sometimes form very distinctive, characteristic shapes. Crystal habit is also greatly determined by the environmental conditions under which a crystal develops.

At the surface of the Earth we generally do not find very much solid rock. The solid rock is covered by several feet of ground up, weathered rock known as regolith, or dirt. However, in some cases, this solid rock does protrude out of the ground in what is known as an outcropping. In order to better understand the some 3,700 different types of known rocks, scientists group them into three groups based on how they are similar and how they are igneous rock, sedimentary rock, and metamorphic rock.

Gems - Mineral Crystals Part I

Gems, precious crystals, rainbow hued fire. Mankind has long sought these precious rocks, often delving deep into the earth; often fighting and bleeding to wrest the gleam from the ground or from another man’s hand. Gems are firmly rooted in our human history. So, what are gems?

Gems are rare mineral crystals valued for their beauty. Historically, gems have been classified as either precious or semi-precious stones. The definitions of precious and semi-precious stones have changed over time and according to culture. For example, the ancient Greeks thought amethyst was a precious stone; however, today amethyst is regarded as a semi-precious stone because we’ve found so many of them in South America. Today, when people talk about precious gems they are usually referring to diamonds, rubies, sapphires, and emeralds. Sometimes pearls (not really a mineral but still called a gem), and opal are considered to be precious gems. It’s misleading to classify gems as either precious or semi-precious. For example, garnet is a semi-precious stone but green garnet can be far more valuable than the same size mid quality emerald. It’s all very confusing. That’s why it is better to use other ways to classify gems.

The best way to classify gems is based on their physical properties. Gems are made from different chemicals and minerals. Because they are made from different things, gems have different physical properties. If you can figure out what a gem is made from you can figure out what kind of gem you have. Diamonds are made from carbon. Rubies and sapphires are made from the mineral corundum. Emeralds are from the mineral beryl and amethysts from the mineral quartz. Rubies have tiny amounts of the element chromium that makes them red. Sapphires are gem quality corundum in any color other than red. Sapphires have tiny amounts of other chemicals that change the color of the crystal. Other gems are made from different mineral crystals.

Remember, sapphires and rubies are made from the same mineral. It could be confusing to tell them apart unless you can see the color of the gem. Color is one way people can tell one gem from another. However, you can’t just use color, there are green garnets and green emeralds. You have to use more than one test to tell one gem from another. There's a big long list of different properties and tests for each of them. There is an entire branch of science that studies gems. The science is called gemology and the scientists are called gemologists. There are laboratories around the world that classify gems, and grade their quality.

Gems - Mineral Crystals Part II

As I said before, gems have played a role in our history. There are many famous gems. There are some gems that are famous for their size or their extraordinary color. Usually both. I am going to talk about a couple of the most famous.

The most famous gem in the world is the Hope Diamond. The Hope Diamond is a very large blue-white diamond currently owned by the Smithsonian Museum in Washington DC, United States. It is the second most visited work of art in the world. The Hope Diamond has been bought, sold and stolen many times since it was discovered in India. At one point it belonged to the kings and queens of France. It was stolen from France during the French Revolution. The people that stole the gem had it re-cut to disguise it then sold it in England. The Hope Diamond was eventually sold to people in the United States who sold it to the Smithsonian Museum.

The next most famous gems are the so-called “Crown Jewels.” When people talk about the “Crown Jewels,” they are usually talking about the Crown Jewels of the United Kingdom specifically. The Crown Jewels are not a pile of jewels, per se. They are the gem studded royal regalia worn by the king or queen of the United Kingdom during coronation and other very rare ceremonies. Regalia is a fancy word for fancy clothes worn by the king or queen. The Crown Jewels include crowns, swords, jewelry, scepters, and the Koh-i-noor. The Koh-i-noor was once the largest known diamond in the world. It is a very large white diamond. I like the look of the hope diamond better. I like the blue color. I think white diamonds are very boring; however, I know that most people like diamonds.

The Crown of Queen Elizabeth the Queen Mother. She wore it with the arches removed at her daughter's coronation in 1953. (You can seen the large Koh-i-noor diamond in the center above another slightly smaller diamond.) Dating from 1661, the Sovereign's Sceptre with Cross signifies temporal power. The sceptre is 92.2cm (36.2 inches) long. Precious stones include the 530 carat Cullinan I diamond. Most of the famous gems are diamonds. I really don’t know why. There’s some kind of crazy mystique that surrounds diamonds. Diamonds are made from carbon, one of the most common elements on earth. Because diamonds made from carbon they are actually very common compared to other gemstones. Diamonds are only expensive because of very good advertising and a company called De Beers of Amsterdam. De Beers rigidly controls the diamond trade. Basically, De Beers owns so many diamonds and diamond mines that if you try to sell diamonds without following their rules they will flood the market with diamonds and drive the price of diamonds down and drive you right out of business.

The Rock Cycle

There are three main types of rocks: igneous, sedimentary, and metamorphic. Each of these types of rocks are formed in different ways and each type of rock can be changed into each of the other types of rock. Geologists call this process the Rock Cycle. Essentially the rock cycle is the process that makes and recycles rocks.

Most rocks on earth began as igneous rocks. Igneous rocks are formed from magma. Magma cools and solidifies into rock. When igneous rocks are exposed on the surface, time and weather break the rock down into smaller and smaller pieces. This process is called weathering and erosion. Wind and water carry the smaller pieces of igneous rocks into piles called sediment beds. Over time the sediment beds get buried and the pieces of rock become cemented together to form a new type of rock called a sedimentary rock.

Our igneous rock has turned into a sedimentary rock. If our sedimentary rock is exposed at the surface, it can be eroded away and eventually changed into new sedimentary rock. However, if our sedimentary rock gets buried deep in the Earth, heat and pressure essentially bake the rock, changing it into something new. This process is called metamorphosis, and the new rock is called a metamorphic rock. Metamorphosis can happen to igneous rocks as well.

Metamorphic rocks can also be weathered and eroded and eventually changed into sedimentary rocks. Or, if metamorphic rock is forced deeper into the Earth, the rock can melt and become magma. If the magma cools and hardens it will form into igneous rock. Igneous rocks and sedimentary rocks can also be forced deep into the earth and melt into magma. Once magma cools it forms igneous rocks.

The rock cycle starts with new rocks formed along what scientists call divergent plate boundaries. “Divergent plate boundaries” is science speak for big cracks in the crust of the earth where the plates are pulling apart. The crust pulls apart and magma pushes up from the mantle, cooling down and forming new rock. Since this type of activity usually takes place on the bottom of the ocean, it is often called sea floor spreading. As the new rock is formed it pushes the old rock to the side like a giant conveyor belt with the oldest rock on the edges and the newer rocks in the middle. On the outside edge of where the plates crash into each other, one of three things happens: The plates either pile up onto each other forming giant mountain ranges, like the Himalayas; one plate dives under another plate, like the Marianas trench (in the western Pacific Ocean); or the plates grind past each other, like they do at the San Andres fault.

When the plates crash into each other, geologists call this type of plate boundary a convergent boundary. When one plate dives under another plate, geologists call this convergent boundary a subduction zone. Subduction zones are an important boundary in the rock cycle. At this boundary, all of the different type of rocks are recycled into new rocks. As the plate is pushed deep into the mantle the rocks are melted into magma. The magma created at subduction zones can form volcanoes near the boundary, cool near the surface and form intrusive igneous rocks, or potentially be carried by currents deep in the mantle to the divergent plate boundary and eventually form igneous rock as a part of sea floor spreading, taking the process right back to the beginning. The rock cycle is the name for the processes that forms and recycles the different types or rocks on our planet. Rocks begin the cycle as igneous rocks, erode into sedimentary rocks then change into metamorphic rocks, finally the rocks melt back to magma and start the process again.

Igneous Rocks

All rocks on Earth were initially igneous in nature. Igneous rocks form as liquid magma cools, forming crystal structured rocks. There are many different types of igneous rocks. Igneous rocks that form deep within the Earth’s crust where temperatures are very high might take thousands of years to cool down. This causes the crystals to be much larger, such as in the case of granite. Igneous rocks formed on the surface cool down in just a matter of a few hours. The crystals in these rocks can be microscopically small.Thus, scientists divide igneous rocks into two different categories: Those which cooled below the surface, and those that cooled on the surface. Those which began their lives below the surface are called intrusive rocks, while those which cooled on the surface are referred to as extrusive rocks.

Igneous rocks are born in fire. There are two types of igneous rocks. The first type and most common is the intrusive igneous rocks. These rocks form when a pocket of magma slowly cools down enough to form into solid rock.

The first thing that we need to know about rocks is: rocks are created from minerals. When a liquid cools to a solid, the substance is said to have crystallized. This means as magma cools, the elements in the magma form solid bonds with their neighbors in a repetitive pattern. The minerals form into bigger and bigger crystals until they smash into other crystals. Once enough mineral crystals smash together so hard that they can't be taken apart, the minerals have formed into an intrusive igneous rock. A great example of this type of rock is granite.

Intrusive igneous rock has coarse grained crystals. That means, if you look closely at the rock you can see the mineral crystals. If you look closely at a piece of granite you will see little flecks of white, black, gray, and sometimes pink. These flecks of color are crystals. If you can see the crystals that form an igneous rock, you're looking at an intrusive igneous rock.

The second type of igneous rock is called extrusive igneous rock. When magma reaches the surface of the earth people call it lava. Extrusive igneous rocks are formed when lava cools and forms into solid rock. This cooling is much faster than the slow cooling that forms intrusive igneous rocks. Extrusive igneous rocks have small grained crystals. Yes, they have crystals; they're just so small you can't see them. There are many different types of extrusive igneous rocks. The type of rock you get depends on what kind of lava the rock was formed from, and how fast the rock cooled.

Magma erupts to the surface becoming lava. The place that magma erupts to the surface is called a volcano. There are three main kinds of volcanoes and each produces their own kind of extrusive igneous rock. If the lava was formed at a high temperature and has a lower amount of silicon (the main ingredient of the mineral quartz), the lava will flow relatively smoothly and cool to form the rock basalt. The type of volcano that produces this kind of lava is called a shield volcano. The volcanoes in Hawaii are shield volcanoes and most of the rock they produce is basalt. When shield volcanoes erupt they normally don't explode. The lava flows up from inside the planet and pours down the side of the volcano like a thick hot syrup. These lava flows cover a large area and are very destructive to property. However, these volcanoes are less dangerous to people because the lava flows are usually very slow.

Stratovolcanoes

A second type of volcano is called a stratovolcano. Stratovolcanoes are created by alternating layers of volcanic ash and other broken up bits of igneous rock covered by layers of solid igneous rock formed from lava flows. The lava from stratovolcanoes is thicker and cooler than the lava from shield volcanoes. But don't let that fool you; stratovolcanoes are far more dangerous and more common than shield volcanoes. The reason stratovolcanoes are so dangerous is: when they erupt, they erupt with a violent explosion that hurls thousands of tons of hot igneous rock, ash, and gas into the air. Sometimes these eruptions form columns of a hot gas and rock mixture. When the column cools enough that it can no longer support its own weight it falls back down, flowing down the sides of the volcano in a scorching hot flow called a pyroclastic flow. These flows are usually 1000ºC (1832ºF) and travel at about 700 kph (435mph). It was a pyroclastic flow that destroyed the ancient cities of Pompeii and Herculaneum in 79CE.

Igneous rocks formed by stratovolcanoes have a lot more silica (mineral quartz) in them. An example of this kind of rock is called rhyolite. Rhyolite is almost the same rock as granite, the only difference is the magma that formed granite was able to cool down slow enough to form large crystals: because rhyolite was exposed to the air, it cooled faster so large mineral crystals were not able to form.

The third and last kind of volcano is called a cinder cone. (This is the kind of volcano you would make for your science fair.) Cinder cone volcanoes are essentially big piles of ash and rocks formed by splattering lava. Pumice and rhyolite are common rocks made by this type of volcano. Igneous rocks are the most common of the rocks that make up the crust. About 95% of the rocks that make up the crust of the planet are igneous rocks. Igneous rocks are the beginning of the rock cycle. The rock cycle is how the crust of our planet is formed and recycled.

Sedimentary Rocks

Over the course of millions of years, the igneous rocks are weathered down by forces of wind and water. Fine particles of dirt begin to cover the landscape. Often, these small rock particles end up being suspended in water, and find their way to the bottom of lakes, streams, and the ocean. Slowly, the layer of sediment on the bottom of lakes, and especially on the bottom of the ocean grows deeper and deeper, reaching depths of thousands of feet. The weight of all the sediment becomes immense, pushing down on lower layers of sediment with tremendous force. In addition, a number of minerals, which act like cement, bond the sediment together, causing it to form sedimentary rock.

Sedimentary rocks are formed from the broken down pieces of other rocks or debris cemented together by intense pressure and minerals deposited by water. There are many kinds of sedimentary rocks. Scientists divide the types of sedimentary rocks into four kinds. These are: clastic, biochemical, chemical, and other. We will talk about each kind. Over time water, wind, heat, and ice wear the rock down causing it to fall apart. This process is called weathering and erosion. The weathered bits of rock are carried by what geologists call agents. Agents are streams, rivers, wind, glaciers, or really anything else that carries the bits of weathered rock away from the large rock that formed them. The most common agent is water in the form of streams or rivers. The weathered bits of rock are carried by the agent until the agent can't move them anymore. The weathered bits of rock pile up into a big pile. The weathered rocks are called sediments. The pile is called a sediment bed. Sediments are usually classified by size: Gravel is the biggest, sand is the next smallest, followed by mud, and silt is the smallest.

Clastic sedimentary rocks are sedimentary rocks formed out of broken down bits of rocks. There are several kinds of clastic sedimentary rocks; they are categorized by the size and sometimes the shape of the pieces that make up the rock. The kinds of clastic sedimentary rocks are called: Conglomerates, breccias, sandstone, mudstone, siltstone. Conglomerates are made from bits of rounded gravel that were deposited by the agent, usually water. Over time the wet pile of sediments becomes so heavy that the gravel gets compacted together, and minerals in the water cement the bits of gravel together. The only difference between conglomerates and breccias is: Conglomerates are made from rounded gravel and breccias are make from angular gravel.

Sandstone is basically the same. Piles of sand are piled up by water or wind and over time the piles get so heavy the sand is pressed together and cemented by minerals found in ground water. There are some interesting things that can be found in sandstone. Fossils are often found in sandstone. Also, have you ever been to the beach or a lake and looked out into the water and noticed that the sand is piled up in ripples by the motion of the waves? Sometimes the sand will get buried and the ripple pattern is preserved. Over time the sand will harden into rock and the ripple marks will still be in the rock. I have found this “ripple marked” sandstone. Somewhere in my house I still have some.

Sometimes sand dunes will become so large they harden into rock preserving the hump shape of the sand dune. There is a very famous fossil that was found in China in one of these preserved sand dunes. The fossil is called the “fighting dinosaurs.” Paleontologists think a velociraptor and protoceratops were fighting and were trapped by a collapsing sand dune.

Mudstone is the same as sandstone except the particles of rock that make up the mudstone are too small to be called sand. As the name sounds, the rock used to be mud that was buried and hardened into rock. Siltstone is made from even smaller particles than mudstone. Fossils can also be found in mudstone and siltstone. These types of rocks are sometimes called slate. In the United States, the national monument named Fossil Butte is near mudstone and siltstone formations that hold hundreds of fish fossils.

Like “ripple marked” sandstone, mudstone can have marks made by water on it. Sometimes when mud hardens the surface cracks; these cracks can be preserved and harden into rock. Even more rare, the marks made by falling raindrops will be preserved in the rock. I have found the mud crack-marked rocks, but not the rain-marked rocks. I'll have to keep looking.

Biochemical sedimentary rocks are formed from the debris of life. For example, limestone is formed from out of decayed animal shells. Animals use calcium to form their shells. After the animal dies, the shell falls apart and the calcium combines with other elements and minerals and hardens into rock. Fossils are very common in this type of rock. I have found fossil trilobites in this rock. Another example of this type of rock is coquina. Coquina is formed from pieces of seashells cemented together. My geology professor had some, it was really neat to look at. Coal and chert are also common biochemical sedimentary rocks.

Chemical sedimentary rocks are formed when water evaporates and leaves behind minerals that harden into rock. A great example of this kind of rock is salt. So remember when you're eating salt, you're eating a rock. It's a rock called halite.

The other category of sedimentary rock is very rare, usually caused by an impact like an asteroid. The asteroid hits so hard it breaks up rocks and fuses them together into a new sedimentary rock. Another example is hot rock spewed from a volcano, but not hot enough to melt the rock it touches; it hardens around other bits of rock forming a new sedimentary rock. Like I said, this is very rare.

Sedimentary rocks only form about 8 percent of the rocks on Earth that cover the other types of rocks like a thin coat of paint. Even though they are only a tiny percentage of the rocks on Earth, they are very important. They tell us a lot about the history of life on earth because sedimentary rocks are the only type of rock that can hold fossils and they are formed in layers with the oldest rocks on the bottom and the newest rocks on the top.

Metamorphic Rocks

Metamorphic rocks form deep within the Earth when heat and pressure are applied to either igneous rocks or sedimentary rocks. This heat and pressure in essence cooks the rocks, changing their structure substantially. The rocks are partially melted and the chemicals within them are rearranged so that the final rock is very different than the original rock.

The final state of a metamorphic rock depends on the amount of pressure the rock was subjected to, the amount of heat the rock was subjected to, and the amount of time the rock was subjected to pressure and heat.One very common metamorphic rock is marble. Marble is formed when heat and pressure are applied to limestone for many thousands of years.

Metamorphic Rock Process

Metamorphic rocks are formed when rocks are changed under heat and intense pressure. Of the rocks that form the continental land mass, most are metamorphic rocks. There are three different ways rocks can be changed by heat and pressure. The process of changing is called metamorphism.

The first kind of metamorphism happens when rocks simply get buried by new rocks formed on top of them. The weight on top of rocks forces them deeper into the earth. The deeper the rocks are pushed into the ground the more they become exposed to heat. The heat and pressure cause the rock to change into a new rock. This type of metamorphism is called regional metamorphism and is the most common form of metamorphism. However, if the heat melts the rock and then the rock cools down it is an igneous rock, not a metamorphic rock.

Another way metamorphic rocks form is called contact metamorphism. Sometimes magma pushes its way up through the crust along cracks in a rock formation. As the magma cools it forms igneous rock. This kind of geologic feature is called an igneous intrusion. Although the rock in the intrusion is igneous rock, the rock the magma contacts can be changed by the heat of the magma and the pressure of the surrounding rock.

Scientists call the third way metamorphic rocks form a tectonic process. Sometimes I think scientists like to use long words to make it harder for non-scientists to figure out what they are talking about. Here's what they are talking about: The large plates that make up the crust of the earth are always moving. Sometimes they slam into each other. Sometimes they grind past each other. Sometimes the plates are pulling apart forming large cracks called rifts. When plates pull apart it is called a divergent boundary. On some boundaries one plate dives under another plate. Geologists call this type of boundary a convergent boundary. When the plates bump and grind past each other, the geologists call this boundary a transform fault boundary. A famous example of this type of fault in the United States is called the San Andres Fault. At that plate boundary, the North American plate is moving mostly south and the Pacific plate is moving mostly north, which means that in 15 million years Los Angeles and San Francisco will be neighbors. I wonder if that will solve the debate about which is the better town. In any case, metamorphic rocks are formed from the pressure and heat caused by the plates crashing into each other.

So what rocks are metamorphic rocks? Examples of these rocks are marble, schist, slate, gneiss (pronounced "nice"). All of these rock types are formed by heat and pressure. So what makes them different? The answer is simple. Metamorphic rocks are formed from different rocks. Marble is made from sedimentary rock called limestone and sometimes dolomite. Gneiss is formed from ingenious rock, like granite. Schist is formed from sedimentary rocks like mudstone or siltstone. Slate is formed from shale. As a matter of fact, slate and shale look so much like each other, the best way to tell them apart is to lightly tap them with a metal object like a coin. Slate and shale make different sounds when tapped. When tapped, slate has a slightly more metallic sound than shale. Shale makes a kind of hollow thumping sound.

Metamorphic rocks are one of the three main types of rocks and are the most common of rock on the continental plates. Fossils may be found in metamorphic rocks, but only if the metamorphic rock was formed from a sedimentary rock that already had the fossil in it. However, the fossil is most likely going to be crushed, warped, or somehow changed because the process that changes sedimentary rock into metamorphic rock will change the fossil, too. Marble is a metamorphic rock used by artists to create sculptures and to decorate buildings and other things. Slate was used to make chalkboards and is still used to make pool tables. Keep your eyes open! Metamorphic rocks are everywhere.

Distribution of Rock Types

Of these three rock types, the most common near the surface of the crust is sedimentary rock. This is due to the many rivers, lakes, and seas that have covered the surface at one time or another. This layer of sedimentary rock is very thin, however, extending downward only a mile or so in depth. Below this sedimentary rock and also mixed with it in many locations is igneous rock. The bulk of the Earth’s crust is made up of both igneous rock and metamorphic rock.

Gold

Forced up from deep inside the earth riding a jet of superheated water surrounding a core of hot liquid rock, untold riches have been deposited in cracks and fissures near the surface of the Earth, waiting for someone to find them. Precious metals are hidden deep in the bowels of the mountains. Gold, silver, platinum, and others have all been deposited in mountains all over the world. Each process that deposits these metals is at the same time unique and surprisingly the same.

Gold is a very interesting metal; it is one of the few metals yellow in color. Gold has physical properties that make it very desirable to people. First, it is pretty. People have liked the glimmer and shine of gold for longer than recorded history. Second, it is malleable. Malleable means that it is easy to shape. Third, it is ductile. Ductile means it can be stretched into a thin sheet or wire. Fourth, it conducts electricity.

A deposit of gold is a concentration of gold in the same area or in the same rock formation. Gold miners really like gold deposits and work really hard to find them. There are two main types of gold deposits: Primary deposits, and Secondary deposits. There is a third type of gold deposit that geologists do not fully understand. It is called the Carlin-type gold deposit and is named after the first miner that found it.

Primary deposits are concentrations of gold inside rock. There are two main types of primary gold deposits. The first type is lode deposits. Load deposits are formed by the same type of events that form mountains. Here is how it happens: When the earth’s plates crash together they pile up on top of each other and form mountain ranges. Sometimes extremely hot water is forced up from deep inside the earth. The extremely hot water flows up through the cracks in the rocks. These cracks are called faults. The water contains lots of minerals and elements. As the water travels through the rock, it cools down. As the water cools it cannot hold onto the minerals. The minerals “fall out” of the water and are deposited along the cracks and fissures in the rock. Gold and quartz are often found together because they both get deposited in cracks in the rock though this process.

The second type of primary gold deposit is very similar to the first. The second type of primary gold deposit is called intrusion related. Here is how it works: Hot magma is sometimes forced up from deep inside the earth. As it rises from deep underground it forces its way up though the rock, sometimes following faults, sometimes just simply melting its way though. As the magma cools down it forms igneous rock. This type of rock formation is called an igneous intrusion. Sometimes as the magma forces it way to the surface it draws extremely hot water with it. Just like before, as the water cools, minerals fall out of the water and are deposited along they way. I can almost here you ask, if the water is right next to magma why doesn’t it just boil away? Magma is so much hotter than the boiling point of water. That’s true, but the water is under so much pressure that it stays liquid long after it should have boiled away. Secondary deposits are called secondary because erosion and water carry the gold from a primary deposit and deposit the gold in a different location. Secondary deposits are divided into two types: Placer and Laterite deposits.

Placer deposits are formed when water crumbles the rock and sweeps the gold downstream. Gold is very heavy for its size so the water has to be moving pretty fast in order to carry the gold downstream. When the water slows down enough, the gold settles to the bottom of the stream. The best place to find gold in the water is where the river slows down - like behind a big boulder, or as the river bends. The most famous kind of gold mining is used to find placer gold. The method is called panning for gold. The idea behind panning for gold is pretty simple. You load up a high-sided metal or plastic pan with dirt you hope has gold in it. Fill the rest of the pan with water. You shake the pan in such a way that the heaviest stuff (gold) in your dirt falls to the bottom of the pan. As you continue to shake the pan you carefully dump the mud and water out of you pan until just the heaviest stuff remains at the bottom. You have to carefully pick out the rocks and make sure they are just rocks. Keep working until you have washed out all the dirt and are just left with gold. It sounds simple, but I have personally never tried it so I don’t know how easy it really is. I think it takes a lot of practice; otherwise you might end up washing the gold out of the bottom of the pan along with everything else.

Laterite deposits are also formed from erosion. Many of these laterite deposits are the leftovers after the main primary deposit has been almost entirely eroded away. Laterite deposits may also be flecks of gold so broken down and so small they have been carried away by weathering and worked into the dirt.

Carlin-type deposits are not very well understood yet. It seems that these types of deposits are also formed by very hot water carrying gold up from deep in the earth. Unlike the other primary types of gold deposits, Carlin-type deposits are found in sedimentary rocks. Another unusual feature of Carlin-type deposits is: unlike other types of primary deposits where you can see the veins or gold running though the rock, Carlin-type gold veins are so small they can only be seen with a microscope. The gold bearing rock has to be crushed up and the gold collected by chemicals before it can be turned into usable metal. There is a lot of metal to be found in these types of deposits, but they have been overlooked in the past because people literally couldn’t see the gold.

Gold is a precious metal that has been forced up from deep in the earth and deposited in primary deposits called lode or igneous intrusion deposits. The primary deposits are broken down by weathering and erosion and carried away by water to either become placer deposits or Laterite deposits. For years and years people have been mining these deposits seeking the shiny precious gold. Only recently have people started to realize that there may be more gold out there, a lot more gold in Carlin-type deposits.

Geologic Time

How old are you? To you, your lifespan probably seems like a large amount of time. The span of just ten years seems like an eternity. As you grow older, time seems to pass more quickly. Consider your grandparents. How old are they? How long ago were your great-grandparents born? Looking way back into history, how long ago did the Egyptians build the pyramids?

To us, as humans, the Egyptian Empire existed in ancient history. To the Earth, however, it happened in just the blink of an eye ago. The Earth as been evolving and changing for many hundreds of millions of years, even billions of years.

The changes that take place in the Earth’s landscape are usually very slow by human standards. It takes many generations of lifetimes before any noticeable changes have taken place in the landscapes of a particular location. Yet, in geologic time, the Earth is constantly changing and evolving. What we see today will be very different in the future. The mountains, rivers, lakes and land formations of today will not exist at some point in the distant future.

Fossil Fuels

There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many years ago before the time of the dinosaurs – hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. "Carboniferous" gets its name from carbon, the basic element in coal and other fossil fuels. The Carboniferous Period occurred at the time, the land was covered with swamps filled with huge trees, ferns and other large leafy plants, similar to the picture above. The water and seas were filled with algae – the green stuff that forms on a stagnant pool of water. Algae is actually millions of very small plants.Some deposits of coal can be found during the time of the dinosaurs. For example, thin carbon layers can be found during the late Cretaceous Period – the time of Tyrannosaurus Rex, however the main deposits of fossil fuels are from the Carboniferous Period. As the trees and plants died, they sank to the bottom of the swamps of oceans. They formed layers of a spongy material called peat. Over many hundreds of years, the peat was covered by sand and clay and other minerals, which turned into a type of rock called sedimentary. More and more rock piled on top of more rock, and it weighed more and more. It began to press down on the peat. The peat was squeezed and squeezed until the water came out of it and it eventually, over millions of years, it turned into coal, oil or petroleum, and natural gas.

Fossil fuel is a general term for buried combustible geologic deposits of organic materials, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth's crust over a long period of time. Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. Fossil fuels contain high percentages of carbon and include coal, petroleum and natural gas. Other more commonly used derivatives of fossil fuels includekerosene and propane. They range from volatile materials with low carbon:hydrogen ratios like methane, to liquid petroleum to nonvolatile materials composed of almost pure carbon, like anthracite coal. Methane can be found in hydrocarbon fields, alone, associated with oil, or in the form of methane clathrates. The theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in the Earth's crust over many years was first introduced by Georg Agricola in 1556 and later byMikhail Lomonosov in the 18th century.

Petroleum and natural gas are formed by the anaerobic decomposition of remains of organisms including phytoplankton and zooplanktonthat settled to the sea (or lake) bottom in large quantities under anoxic conditions, millions of years ago. Over geological time, this organicmatter, mixed with mud, got buried under heavy layers of sediment. The resulting high levels of heat and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. There is a wide range of organic, or hydrocarbon, compounds in any given fuel mixture. The specific mixture of hydrocarbons gives a fuel its characteristic properties, such as boiling point, melting point, density, viscosity, etc. Some fuels like natural gas, for instance, contain only very low boiling, gaseous components. Others such as gasoline or diesel contain much higher boiling components. Terrestrial plants, on the other hand, tend to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas

Non-fossil sources in 2006 included hydroelectric, nuclear, and others (geothermal, solar, tidal, wind, wood, waste). World energy consumption was growing about 2.3% per year.

Although fossil fuels are continually being formed via natural processes, they are generally considered to be non-renewable resourcesbecause they take so many years to form and the known viable reserves are being depleted much faster than new ones are being made. The use of fossil fuels raises serious environmental concerns. The burning of fossil fuels produces around 21.3 billion tonnes (21.3gigatonnes) of carbon dioxide (CO2) per year, but it is estimated that natural processes can only absorb about half of that amount, so there is a net increase of 10.65 billion tonnes of atmospheric carbon dioxide per year (one tonne of atmospheric carbon is equivalent to 44/12 or 3.7 tonnes of carbon dioxide). Carbon dioxide is one of the greenhouse gases that enhances radiative forcing and contributes to global warming, causing the average surface temperature of the Earth to rise in response, which the vast majority of climate scientistsagree will cause major adverse effects. A global movement towards the generation of renewable energy is therefore under way to help reduce global greenhouse gas emissions.

The principle of supply and demand holds that as hydrocarbon supplies diminish, prices will rise. Therefore, higher prices will lead to increased alternative, renewable energysupplies as previously uneconomic sources become sufficiently economical to exploit. Artificial gasolines and other renewable energy sources currently require more expensive production and processing technologies than conventional petroleum reserves, but may become economically viable in the near future. Different alternative sources of energyinclude nuclear, hydroelectric, solar, wind, and geothermal.

Coal

Coal is a hard, black colored rock-like substance. It is made up of carbon, hydrogen, oxygen, nitrogen and varying amounts of sulphur. There are three main types of coal – anthracite, bituminous and lignite. Anthracite coal is the hardest and has more carbon, which gives it a higher energy content. Lignite is the softest and is low in carbon but high in hydrogen and oxygen content. Bituminous is in between. Today, the precursor to coal—peat—is still found in many countries and is also used as an energy source.

The earliest known use of coal was in China. Coal from the Fu-shun mine in northeastern China may have been used to smelt copper as early as 3,000 years ago. The Chinese thought coal was a stone that could burn.

*While this video cites millions of years for the formation of coal we would like to remind you that time varietions are still under scrutiny by many scientists and cannot be fully determined as absolute.

Coal is found in many of the lower 48 states of U.S. and throughout the rest of the world. Coal is mined out of the ground using various methods. Some coal mines are dug by sinking vertical or horizontal shafts deep under ground, and coal miners travel by elevators or trains deep under ground to dig the coal. Other coal is mined in strip mines where huge steam shovels strip away the top layers above the coal. The layers are then restored after the coal is taken away. The coal is then shipped by train and boats and even in pipelines. In pipelines, the coal is ground up and mixed with water to make what's called a slurry. This is then pumped many miles through pipelines. At the other end, the coal is used to fuel power plants and other factories.

Oil or Petroleum

Oil is another fossil fuel. It was also formed more than 300 million years ago. Some scientists say that tiny diatoms are the source of oil. Diatoms are sea creatures the size of a pin head. They do one thing just like plants; they can convert sunlight directly into stored energy. In the graphic on the left, as the diatoms died they fell to the sea floor. Here they were buried under sediment and other rock. The rock squeezed the diatoms and the energy in their bodies could not escape. The carbon eventually turned into oil under great pressure and heat. As the earth changed and moved and folded, pockets where oil and natural gas can be found were formed. Oil has been used for more than 5,000-6,000 years. The ancient Sumerians, Assyrians and Babylonians used crude oil and asphalt ("pitch") collected from large seeps at Tuttul (modern-day Hit) on the Euphrates River. A seep is a place on the ground where the oil leaks up from below ground. The ancient Egyptians, used liquid oil as a medicine for wounds, and oil has been used in lamps to provide light.

The Dead Sea, near the modern Country of Israel, used to be called Lake Asphaltites. The word asphalt was derived is from that term because of the lumps of gooey petroleum that were washed up on the lake shores from underwater seeps. In North America, Native Americans used blankets to skim oil off the surface of streams and lakes. They used oil as medicine and to make canoes water-proof. During the Revolutionary War, Native Americans taught George Washington's troops how to treat frostbite with oil.

As our country grew, the demand for oil continued to increase as a fuel for lamps. Petroleum oil began to replace whale oil in lamps because the price for whale oil was very high. During this time, most petroleum oil came from distilling coal into a liquid or by skimming it off of lakes – just as the Native Americans did.

Then on August 27, 1859, Edwin L. Drake (the man standing on the right in the black and white picture to the right), struck liquid oil at his well near Titusville, Pennsylvania. He found oil under ground and a way that could pump it to the surface. The well pumped the oil into barrels made out of wood. This method of drilling for oil is still being used today all over the world in areas where oil can be found below the surface.

Oil and natural gas are found under ground between folds of rock and in areas of rock that are porous and contain the oils within the rock itself. The folds of rock were formed as the earth shifts and moves. It's similar to how a small, throw carpet will bunch up in places on the floor. To find oil and natural gas, companies drill through the earth to the deposits deep below the surface. The oil and natural gas are then pumped from below the ground by oil rigs (like in the picture). They then usually travel through pipelines or by ship. Oil is found in 18 of the 58 counties in California. Kern County, the County where Bakersfield is found, is one of the largest oil production places in the country. But we only get one-half of our oil from California wells. The rest comes from Alaska, and an increasing amount comes from other countries. In the entire U.S., more than 50 percent of all the oil we use comes from outside the country... most of it from the Middle East. Oil is brought to California by large tanker ships. The petroleum or crude oil must be changed or refined into other products before it can be used.

Refineries

Oil is stored in large tanks until it is sent to various places to be used. At oil refineries, crude oil is split into various types of products by heating the thick black oil.

Oil is made into many different products – fertilizers for farms, the clothes you wear, the toothbrush you use, the plastic bottle that holds your milk, the plastic pen that you write with. They all came from oil. There are thousands of other products that come from oil. Almost all plastic comes originally from oil. Can you think of some other things made from oil?

The products include gasoline, diesel fuel, aviation or jet fuel, home heating oil, oil for ships and oil to burn in power plants to make electricity. Here's what a barrel of crude oil can make.

In California, 74 percent of our oil is used for transportation – cars, planes, trucks, buses and motorcycles.

Natural Gas

Sometime between 6,000 to 2,000 years BCE (Before the Common Era), the first discoveries of natural gas seeps were made in Iran. Many early writers described the natural petroleum seeps in the Middle East, especially in the Baku region of what is now Azerbaijan. The gas seeps, probably first ignited by lightning, provided the fuel for the "eternal fires" of the fire-worshiping religion of the ancient Persians.

Natural gas is lighter than air. Natural gas is mostly made up of a gas called methane. Methane is a simple chemical compound that is made up of carbon and hydrogen atoms. It's chemical formula is CH4 – one atom of carbon along with four atoms hydrogen. This gas is highly flammable. Natural gas is usually found near petroleum underground. It is pumped from below ground and travels in pipelines to storage areas. The next chapter looks at that pipeline system. Natural gas usually has no odor and you can't see it. Before it is sent to the pipelines and storage tanks, it is mixed with a chemical that gives a strong odor. The odor smells almost like rotten eggs. The odor makes it easy to smell if there is a leak.

Natural Gas Distribution System

It is a gaseous molecule that's made up of two atoms – one carbon atom combined with four hydrogen atom. It's chemical formula is CH4. The picture on the right is a model of what the molecule could look like. Don't confuse natural gas with "gasoline," which we call "gas" for short. Like oil, natural gas is found under ground and under the ocean floor. Wells are drilled to tap into natural gas reservoirs just like drilling for oil. Once a drill has hit an area that contains natural gas, it can be brought to the surface through pipes.The natural gas has to get from the wells to us. To do that, there is a huge network of pipelines that brings natural gas from the gas fields to us. Some of these pipes are two feet wide.Natural gas is sent in larger pipelines to power plants to make electricity or to factories because they use lots of gas. Bakeries use natural gas to heat ovens to bake bread, pies, pastries and cookies. Other businesses use natural gas for heating their buildings or heating water.

Through larger pipelines, the gas goes through smaller and smaller pipes to your neighborhood.In businesses and in your home, the natural gas must first pass through a meter, which measures the amount of fuel going into the building. A gas company worker reads the meter and the company will charge you for the amount of natural gas you used.

Energy can be found in a number of different forms. It can be chemical energy, electrical energy, heat (thermal energy), light (radiant energy), mechanical energy, and nuclear energy.In some homes, natural gas is used for cooking, heating water and heating the house in a furnace.In rural areas, where there are no natural gas pipelines, propane (another form of gas that's often made when oil is refined) or bottled gas is used instead of natural gas.

Propane is also called LPG, or liquefied petroleum gas, is made up of methane and a mixture with other gases like butane. Propane turns to a liquid when it is placed under slight pressure. For regular natural gas to turn into a liquid, it has to be made very, very cold. Cars and trucks can also use natural gas as a transportation fuel, but they must carry special cylinder-like tanks to hold the fuel. When natural gas is burned to make heat or burned in a car's engine, it burns very cleanly. When you combine natural gas with oxygen (the process of combustion), you produce carbon dioxide and water vapor; plus the energy that's released in heat and light. Some impurities are contained in all natural gas. These include sulphur and butane and other chemicals. When burned, those impurities can create air pollution. The amount of pollution from natural gas is less than burning a more "complex" fuel like gasoline. Natural gas-powered cars are more than 90 percent cleaner than a gasoline-powered car.That's why many people feel natural gas would be a good fuel for cars because it burns cleanly.