The Rock Presintation
By Yash Sarada
Description of the Rock Cycle
Obsidian is usually an extrusive rock, one that solidifies above Earth's surface. Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. The result is a volcanic glass with a smooth, even texture.
Obsidian can form in a variety of cooling environments:
- along the edges of a lava flow (extrusive)
- around the edges of a sill or a dike (intrusive)
- where lava contacs water (extrusive)
- where lava cools while airborne (extrusive)
Obsidian rocks can be found in Argentina, Armenia, Canada, Chile, Greece, Iceland, Italy, Kenya, Mexico, New Zealand, Peru, Scotland, and the United States.
Slate is a fine-grained rock that is created by the alteration of shale or mudstone by low grade metamorphism. It is popular for a wide variety of uses such as roofing, flooring and flagging because of its durability and pretty appearance.
Shale and mudstone are in a basin and are compressed by horizontal forces with minor heating. These forces and heat modify the clay minerals in the shale and mudstone. Foliation develops at right angles to the compressive forces of the convergent plate boundary to yield a vertical foliation that usually crosses the bedding planes that existed in the shale.
Slate is found in Brazil, United States, Africa, Spain, and China.
Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment. Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels. Coal has a wide range of uses; the most important use is for the generation of electricity.
Most of our coal was formed about 300 million years ago, when much of the earth was covered by steamy swamps. As plants and trees died, their remains sank to the bottom of the swampy areas, accumulating layer upon layer and eventually forming a soggy, dense material called peat. Over long periods of time, the makeup of the earth's surface changed, and seas and great rivers caused deposits of sand, clay and other mineral matter to accumulate, burying the peat. Sandstone and other sedimentary rocks were formed, and the pressure caused by their weight squeezed water from the peat. Increasingly deeper burial and the heat associated with it gradually changed the material to coal.
The biggest supply of coal is found in the United States. Russia, China, New-Zealand/Australia, and India.