Rock types and how they are made.

Write down the things that are underlined, if it is a definition then try to copy it for word. If it is a statement then try to read it and put it into your own words.

Igneous Sedimentary Metamorphic Geology Erosion Deposition Compaction cementation Intrusive Extrusive

To identify a rock a geologist take many things into account in the identifying process. What it looks like where it was found, what minerals are in the rock, and the inside of the rock all play roles in identifying a rock. Why not the outside of the rock? When studying a rock geologist observe the rocks minerals composition, color, and texture.

Most of the rocks in the Earths crust are made of about 20 different minerals. These are known as the rock forming minerals. The different amounts of these minerals is what makes the rocks different from each other, it changes there density, color, and texture. For example granite and basalt are both igneous rock, but granite has much more silica, which changes its color and texture. The size and shape of crystals in rocks are also important clues to identifying a rock.

When looking at a rock the texture is the look and the feel of the rocks surface. Some rocks are smooth and glossy, while other’s are rough and/or chalky. The grain size also plays a role in the texture. There are three different ways grain’s effect texture. Grain size Grain shape Grain pattern

Using color texture and mineral composition, geologist can classify a rock according to its origin. What is origin? Its where and how the rock was formed. There are three major groups we classify rocks into. What are they? Igneous Sedimentary Metamorphic

Forms from the cooling of molten rock at or below the surface. All igneous come from volcanoes, and magma plums. Can anybody give three examples of igneous rock. Granite Basalt Obsidian Pumice Rhyolite Igneous rocks are classified by origin, texture and mineral content.

Igneous rock can form on or under Earths crust. If it formed on top then we call it extrusive. Extrusive : is igneous rock formed from lava that erupted onto Earths surface. Examples: obsidian, basalt, and pumice If it formed under the Earths crust we call it intrusive Intrusive: is igneous rock that formed when magma cooled and hardened beneath Earth’s surface. Examples: granite, and rhoilight

Texture in igneous rocks depends on the crystal structure, except for obsidian =volcanic glass which has no crystalline structure. Intrusive have larger crystals than intrusive and are usually much more cores. Mineral content can determine where it came from, the major mineral is silica.

Sedimentary rock is formed from sediment. Sediment: is small solid pieces of material that come from rocks or living things. Most sedimentary rocks are formed in 4 processes. Erosion: the forces of erosion are heat, cold, rain, waves and grinding. Running water, wind, or ice loosen and carry away the fragments of rock Deposition: The process which sediment settles out of the water or wind that carry it. Compaction: the process that presses the sediment together. Cementation: is the process in which dissolved minerals in the water, crystallize and glue that sediments together.

Clastic rock: is a sedimentary rock that forms when rock fragments are squeezed together. Examples : shale, sandstone, Organic rock: forms where the remains of plants and animals are deposited in thick layers. Examples: coal, limestone. Chemical rock: form when minerals that are dissolved in a solution crystallize. Rock salt, and a special type of limestone.

What does metamorphic mean? In Greek meta means change. And morphosis means form. Heat and pressure deep inside the Earth can change any rock into a metamorphic rock. When a rock changes into a metamorphic rock its texture, crystalline structure, and mineral content change. Geologist classify metamorphic rocks according to the arrangement of the grains that make up the rock.

Metamorphic rock that have there grains arranged in parallel layers or bands are said to be foliated. Examples: slate schist, and gneiss

Nonfoliated rocks have their mineral grains arranged randomly. These do not split into layer’s like slate does. Examples: marble and quartz.