RocksGroup5

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.


 * Igneous rocks**- form when lava or magma cools and minerals crystallize.

Igneous rocks begin as hot, fluid material, the word "igneous" comes from a Greek word for fire.

Igneous rocks are classified as intrusive or extrusive. Intrusive rocks- form when magma cools and crystallizes below earths surface. Granite is an example of a rock that cooled slowly and has large crystals. Extrusive rocks- forms when magma that cools and crystallizes on earths surface. Basalt is an example of this type of rock.

The two best known igneous rock types are basalt and granite.

Igneous rocks differ in the sizes of theirs grains or crystals. The main minerals in igneous rocks are hard, primary ones: feldspar, quartz, amphiboles, pyroxenes and olivines.

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)


 * **Some Common Igneous Rocks** ||
 * **Name** || **Image** || **Color** || **Texture** ||
 * **Granite** || [[image:http://library.thinkquest.org/J002289/images/granite.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/granite.jpg"]] || **Pink/Gray** || **Intrusive** ||
 * **Gabbro** || [[image:http://library.thinkquest.org/J002289/images/gabbro.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/gabbro.jpg"]] || **Dark Gray to Black** || **Intrusive** ||
 * **Rhyolite** || [[image:http://library.thinkquest.org/J002289/images/rhyolite.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/rhyolite.jpg"]] || **Light Pink or Gray** || **Extrusive** ||
 * **Basalt** || [[image:http://library.thinkquest.org/J002289/images/basalt.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/basalt.jpg"]] || **Dark Gray to Black** || **Extrusive** ||
 * **Obsidian** || [[image:http://library.thinkquest.org/J002289/images/obsidian.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/obsidian.jpg"]] || **Usually Dark Colored** || **Extrusive** ||
 * **Scoria** || [[image:http://library.thinkquest.org/J002289/images/scoria.jpg width="75" height="75" align="center" link="http://library.thinkquest.org/J002289/images/scoria.jpg"]] || **Dark Colored** || **Extrusive** ||
 * Sedimentary Rocks**-

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.

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

Metamorphic Rocks- ** When high temperature and pressure combine and change in texture, mineral composition or chemical composition of a rock without melting it. - High temperatures and high pressures come from deep burial

Metamorphic rocks are classified into two textural groups: -Foliated- Layers and band of mineral. High pressure during metaporphism causes minerals that are flat or needlelike crystals to form with their long axes perpendicular to the pressure.



-Nonfoliated-minerals that form with blocky cyrstal. Two examples are quartzite and marble. metamorphic minerals can grow large while the surronding minerals remain the same. Types of Metamorphism: The minerals that form and the degree of change provides information about the different types. - Regional metamorphism- when the high temperature and pressure affect large regions of the earths crust. results of this are change in minerals and rock types, folding and deforming of rock layers. - Contact metamorphism- when molten material comes in to contact with solid rock. characteristics are high temperature and moderate-to-low pressure. - Hydrothermal metamorphism- when very hot water reacts with rock and alters its chemical and mineral composition. chemical changes are common.

Economic Importance of Metamorphic Rocks and Minerals the modern way of life is made possible by a great number of naturally occuring Earth material. -Metallic mineral resources- occur mostly in the form of metal ores. -Non-mtallic resources- since talc is not combustible and has low thermal and electric conductivity,it is used for fireprroof and insulating material.

The continues changing and remarking of rocks -Metamorphic rocks form from change in temperature and pressure. -Any rock can be changed into any other rock.
 * The rock cycle:**