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Friday, April 23, 2010

New to Rocks, Minerals and Fossils?

Sedimentary Rocks

Seventy percent of all the rocks on earth are sedimentary rocks.
The earth's surface is constantly being eroded. This means that rocks are broken up into smaller pieces by weathering agents such as wind, water, and ice. These small pieces of rock turn into pebbles, gravel, sand, and clay. They tumble down rivers and streams. These pieces settle in a new place and begin to pile up and the sediments form flat layers. Over a long period of time, the pieces become pressed together and form solid rock called sedimentary rock. Most sedimentary rocks form under water. Most of the earth has been covered by water some time in the past. 70% of the earth is covered by water now. So sedimentary rocks are common all over the world. Sedimentary rocks are often rich in fossils.
Sediments can harden into sedimentary rock in two ways.
pressure-As layer after layer of sediments are deposited, the lower layers are pressed together tightly under the weight of the layers above. cementing-Some sediments are glued together by minerals dissolved in water.
Some examples of sedimentary rocks are sandstone, limestone, conglomerate, and shale. Sandstone is formed from grains of sand pressed tightly together. Sandstones are very common rocks. They are formed from the sand on beaches, in riverbeds, and sand dunes. Sandstones are usually made of the mineral quartz. Limestone is formed from tiny pieces of shells of dead sea animals that have been cemented together. Conglomerate contains sand and rounded pebbles that have also been cemented together. Shale is formed from mud or clay that has been pressed together. Shale forms in quiet waters such as swamps and bogs. Sedimentary rocks are easy to identify because you can actually see the layers.
This is a summary of the major characteristics of sedimentary rocks:
Classified by texture and composition Often contains fossils May react with acid Often has layers, flat or curved Usually composed of pieces cemented or pressed together Has great color variety Particle size may be the same or vary Usually has pores between pieces May have cross-bedding, mud cracks, worm burrows, raindrop impressions
Here's a checklist of some common sedimentary rocks and their characteristics. Look for these same characteristics in the rocks you find, and you'll be well on your way to becoming a rockhound.
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Igneous Rocks

Digging at a rate of one foot per minute, it will take you 87 years to make a tunnel all the way through Earth.
The oldest type of all rocks is the igneous rock.The word "igneous" comes from a Greek word for fire. Deep inside the earth, the temperature is very high and the minerals there are in liquid form called magma. As the magma pushes towards the earth's surface, it starts to cool and turns into solid igneous rock.
All igneous rocks do not cool the same way. That is why they do not look all the same. Some cool slowly, deep under the earth's surface. These are called intrusive igneous rocks. The slow cooling formed rocks with large crystals. Granite is an example of a rock that cooled slowly and has large crystals.
Other rocks formed when the magma erupted from a volcano or reached the earth's surface through long cracks. Magma is called lava when it reaches the earth's surface. Lava cools quickly and forms rocks with small crystals. They are called extrusive igneous rocks. Basalt is an example of this type of rock. Obsidian is an example of another extrusive igneous rock that cooled so fast that it has no crystals and looks like shiny, black glass.
This is a summary of the major characteristics of igneous rocks:
Classified by texture and composition Normally contains no fossils Rarely reacts with acid Usually has no layering Usually made of two or more minerals May be light or dark colored Usually made of mineral crystals of different sizes Sometimes has openings or glass fibers May be fine-grained or glassy (extrusive)
Here's a checklist of some common igneous rocks and their characteristics. Look for these same characteristics in the rocks you find, and you'll be well on your way to becoming a rockhound.
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Metamorphic Rock

Heat and pressure can change many things. They can even change rocks. The name for rocks that has been changed is metamorphic rocks. Metamorphic comes from Greek words meaning "change" and "form".
Metamorphic rocks form deep in the earth where high temperature, great pressure, and chemical reactions cause one type of rock to change into another type of rock. Metamorphic rocks begin to form at 12-16 kilometers beneath the earth's surface. They begin changing at temperatures of 100 degrees Celsius to 800 degrees Celsius. If you squeeze and heat a rock for a few million years, it can turn into a new kind of rock.
Where does the heat come from? The heat comes from magma. Where does the pressure come from? The pressure comes from layers of rock piled on top of layers and layers of rock. The layers on the bottom get squeezed. The thicker the layers, the more pressure there is.
Some examples of how metamorphic rocks were changed:
Sandstone becomes Quarzite
Shale becomes Slate
Limestone becomes Marble
This is a summary of the major characteristics of metamorphic rocks.
Classified by texture and composition Rarely has fossils May react with acid May have alternate bands of light and dark minerals May be composed of only one mineral, ex. marble & quartzite May have layers of visible crystals Usually made of mineral crystals of different sizes Rarely has pores or openings May have bent or curved foliation.
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What is a Rock?

Rocks found on the moon have some of the same compositions as rocks found on earth.
Can you guess it? What is something that you see everyday... places that you can see are like, mountains, parks, schools, highways, the ground, your backyard, the woods, the forest, contruction sites. They might be small or big. You might even see them around the neck of some kid... Did you guess it?
ROCKS! Thats right, ROCKS!
Rocks are everywhere. They have been on the earth over 4 billion years. Maybe 5 billion years now. The rock you see might have once been part of a magnificent mountain or spectacular cave. It could have even been stomped by a dinosaur. Rocks are a fascinating way to discover information about the history of the earth.
Most rocks are made of minerals. However, all rocks are not the same. That is why rock collecting is so interesting and fun. Every rock has its own story.
Rocks can be put into three basic rock types: igneous, sedimentary, and metamorphic. How a rock is formed determines which group it is placed in.
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Rock Cycle
 Facinating Fact-Up to 100,000 tons of rock a year fall to earth from space. The largest meteorite in the world lies in the ground in Africa and weighs more than 60 tons. Did you know that rocks are constantly being recycled? Recycle means to take something old and then trying to make something new. Of course it doesn't take rocks to change into another rock. It takes millions of years! To understand how this happens, lets take a jouney through the rock cycle. First our journey begins in the mantle. Here we see some red hot magma that is being pushed up towards the crust. Some of this magma creeps into the cracks of the volcano while the rest is just like... Forced to be pushed at the top. Once the magma inside the volcano is out of the volcano, it is called lava. The lava cools and makes igneous rocks. Then some of the igneous rocks roll down the mountains formed by the volcanoes and eventually land inside the ocean. As they roll, bits and pieces of the igneous rock are broken and form sediments. Layer after layer of the sediments are pressed and cemented together forming sedimentary rocks. Some of the sedimentary rocks on the very bottom get hot because of the pressure and change to metamorphic rock. When the metamorphic rock is buried deeper, it gets hotter and melts. Once again, it becomes magma and may eventually may be pushed up and out of the volcano. The rock cycle begins all over again.
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What is a Mineral?
Do you know the difference between a rock and a mineral? Minereals are the building blocks of rocks. Here are some of the basic characteristics of minerals to help you understand are: Minereals are inorganic meaning that they are not alive and is non living. It is not a plant or animal. An example of a rock that is not a mineral is coal. Coal is a substance formed from decayed plants and animals. Therefore, coal is not considered a mineral. Minereals are found in the earth or are really naturally occuring substances. They are found in dirt, rocks and water. They are not made by man. Minereals are chemical substances. Some minereals like gold or silver are made of only one element. Other minerals, like quarts and calcite, are combinations of two or more elements. Minereals always have the same chemical makeup. For example, quarts will always consist of one part cilicon (an element) two parts oxygen (another element). Minereals are usually solid and hard stable crystals. They have numbers of some flat surfaces in a orderly arrangement. For example... A crystal of quarts is always hexagonal because of the way the atoms of silicon and oxygen join together. About 2,000 minerals have been found. Oxygen is part of many minerals. Minerals containing oxygen make up almost half of the earth's crust. Quarts is a common mineral. Other common minerals are feldspar, mica and horneblend. Many rocks are made of these common minerals. Some minerals are very rare and very expensive. These are called "gems." Diamonds, rubies, and emeralds are good examples of such minerals. Gold and silver are also minerals. Together, these natural substances are used to make beautiful, pretty and cute creative jewlery.
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What is a Geologist and a Palentologist?
A Geologist is a person or people who look for different types of rocks and find out what they are called. They look for rock and they travel alot. A Palentologist is a person or people who look for different types of fossils. They try to find out what thing the fossil has on it.
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What is a Fossil?
A fossil is a rock that has bones or track marks on it. It has either a living thing or a nonliving thing. It can have a dead fish stuck onto it and then melts and sticks on very much to the fossils so that only the bones show. The rest of the body is inside the rock. Same thing for shells, snails, plants, dinosaurs, e.t.c.
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