Semester Exam Review Rocks & Minerals

Rocks The 3 types of rocks are: Igneous Sedimentary Metamorpic

Igneous Rocks Igneous rocks are formed when lava or magma cools and hardens. Extrusive igneous rocks form when lava cools on the Earth's surface. A volcano makes extrusive igneous rocks.

Pumice Extrusive igneous rock made of solidified volcanic ash. Full of holes. Floats on water.

Obsidian Extrusive igneous rock. Lava cools in water so it solidifies quickly. Also known as volcanic glass because it looks like glass.

Intrusive Igneous Rocks Form when magma cools slowly under the Earth's surface. Most intrusive rocks have large, well-formed crystals. Examples include granite, gabbro, and diorite. All of these form under the Earth’s surface.

Sedimentary Rocks Sedimentary rocks tell us what the Earth's surface was like in the geologic past. They can contain fossils that tell us about the animals and plants or show the climate in an area.

Chemical Sedimentary Rocks Form from chemical reactions in the oceans, seas, and lakes.

Organic Sedimentary Rocks The sediment in an organic sedimentary rock is made of tiny fossils! Sedimentary rocks are also important because they may contain water for drinking or oil and gas to run our cars and heat our homes. Examples: chalk and limestone

Metamorphic Rocks Any rock can become a metamorphic rock. Metamorphic rocks: rocks buried deep in the Earth that formed at high temperatures and under extreme pressure.

Nonfoliated Metamorphic Rocks Identified on the basis of their composition: Quartzite= composed of the mineral quartz, metamorphosed sandstone. Marble=composed of the mineral calcite; metamorphosed limestone.

Minerals Minerals are naturally occurring, inorganic solids with a definite chemical composition and a characteristic crystalline structure. About 3,000 different minerals have been described.

Mineral Identification Most minerals can be identified by their physical properties: Color Streak Luster Hardness Cleavage Fracture Density Crystal form).

Color Some minerals are easily identified by color because they are never any other color. But, chemical impurities can change the color of a mineral without changing its basic make-up, so it is not a very good way to identify a mineral.

Quartz Quartz constitutes 12% of the Earth's crust and is used in countless products from computers and watches to satellites and medical equipment.

Luster Luster is the way the surface of a mineral reflects light. There are two general types of luster – metallic (ex: gold) and non-metallic.

Hardness Mohs Hardness Scale: Arrangement of 10 minerals into a sequence from 1-10. 1 is the softest mineral, 10 is the hardest mineral.

Fracture & Density Not all minerals cleave easily, some fracture instead. Fractures can be smoothly curved, irregular, jagged or splintery. Each mineral has a unique density which can help to identify it.