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Rocks & Minerals Minerals • There are about 3000 known minerals • Minerals are made of elements (either a single element or a combination of elements) • Examples of Minerals – Gold: a mineral made of one element (gold…Au) – Calcite: a mineral made of elements (calcium, carbon, and oxygen…CaCO3) gold calcite Scientific Requirements for a Substance to be a Mineral • • • • • Must be naturally occurring (they must occur in nature) Must be inorganic (not made of living things) Must be crystalline (have a crystal structure) Must be solid (minerals are not gases and liquids) Must have definite physical and chemical properties How we identify minerals? • By color: a red mineral is most likely not gold (which is a shiny gold color) or biotite (which is a black color) • By luster: the luster of a mineral describes how shiny it looks (silver has a metallic luster and pure quartz has a glassy luster) • By streak color: What color is the streak when a mineral is rubbed on a porcelain plate? • By hardness: How hard is the mineral? (The Mohs hardness scale uses numbers to describe hardness) Mohs Mineral Hardness Scale 1) Talc Softest 2) Gypsum 3) Calcite 4) Flourite 5) Apatite 6) Feldspar 7) Quartz 8) Topaz 9) Corundum 10) Diamond Hardest 10 Rocks • Rocks are mixtures of minerals • Most rocks are composed of at least minerals • Example of a rock: – Granite: contains 75% feldspar, 20% quartz, and 5% mica Classifying Rocks • Rocks are classified by how they formed and what they’re made of • There are general classes of rocks – Igneous Rocks…are formed when lava and magma crystallize to form solid rock – Metamorphic Rocks…are formed when an existing rock is partially melted, squeezed, or both – Sedimentary Rocks…are formed when sediments (sand clay, and silt) are compressed and become solid rock Examples of Different Classes of Rocks Igneous Granite cooled very slowly Obsidian cooled very quickly Examples of Different Classes of Rocks Metamorphic Gneiss has bands because it was folded and compressed Examples of Different Classes of Rocks Sedimentary Sandstone is made of sand grains Shale is made of clay particles
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