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Minerals

Science, Grade 8

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Identifying Minerals Uses of Minerals Mohs Hardness Scale What Is a Mineral? A mineral, by definition, must meet four criteria. It must be a naturally occurring, solid substance that has an internal crystal structure and is formed by inorganic processes. How Do Minerals Form? Minerals form in a wide variety of geologic environments. Some, like garnet, asbestos, talc and kyanite, form as a result of intense heat and pressure created during metamorphism. Some minerals form from hot-water solutions created when ground water is heated by magma. Dissolved metals and other elements in the hot liquid solution crystallize forming new minerals. Other minerals form from liquid rock (magma) as the magma cools. Yet another group of minerals forms as ocean water evaporates. talc gypsum calcite fluorite apatite feldspar quartz topaz corundum diamond 1 2 3 4 5 6 7 8 9 10 Many of the commodities we consume and use every day are mined from rocks and minerals. For example, the element fluorine is used to make fluoride for toothpaste. Copper pipes and wires are made from the copper minerals malachite and cuprite. The steel used to make appliances and cars is a mixture of iron and other metals. Glass windows and drinking glasses are made from quartz sand. Gold is used in computers, cell phones and other electronic equipment. galena (with silver) Crystal System Every mineral forms a specific crystal shape. There are over 3,500 mineral species. All of these species belong to one of seven different crystal systems. The crystal systems are determined by the internal arrangement of the molecules in the mineral. Color Color is sometimes used to help identify a certain mineral. Streak Streak is the color of a mineral when it is crushed to a powder. This is found by rubbing the specimen on a piece of unglazed porcelain. Minerals with hardness greater than 7 do not leave a streak. Luster Luster is a description of how light reflects off of a mineral. Some of the luster descriptions are metallic, glassy (also called vitreous), earthy, adamantine (diamond-like), greasy and dull. Specific Gravity Specific gravity is a measure of the density of a mineral. The density is determined by comparing the mass of the mineral with the mass of an equal amount of water. Hardness A mineral’s hardness is determined by comparing the mineral to the known hardness of the minerals in the Mohs Hardness Scale. Cleavage & Fr acture Cleavage is a description of how a mineral breaks on flat planes. Fracture is a description of how a mineral breaks along curved or irregular surfaces. Special Properties There are also interesting physical properties that are unique to some minerals. For example, hematite always has a deep, blood red streak. Magnetite and lodestone are magnetic. diamond mica Minerals are identified based on their physical properties. gold crystals sulfur amethyst halite tourmaline copper talc a crystal structure (NaCl) magnetite same size - different densities As magma cools, ions in the magma combine to form specific minerals, such as topaz and tourmaline. Halite (rock salt) is the most common mineral formed by the evaporation of salt water. Gold and copper are formed from hot-water solutions. Talc is a mineral that can be found in metamorphic rock. Minerals © Copyright NewPath Learning. All Rights Reserved. 94-4101 www.newpathlearning.com Some photos courtesy of USGS.

Identifying Minerals Uses of Minerals • cleavage • color • crystal structure • fracture • hardness • luster • magma • Mohs Hardness Scale • specific gravity • streak Key Vocabulary Terms What Is a Mineral? __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ How Do Minerals Form? __________________________________________ __________________________________________ __________________________________________ __________________________________________ __________________________________________ __________________________________________ Mohs Hardness Scale 1 2 3 4 5 6 7 8 9 10 __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ Crystal System ________________________ ________________________ ________________________ ________________________ Color _______________________ _______________________ _______________________ Streak ____________________ ____________________ __________________________________ Luster _______________________ _______________________ _______________________ Specific Gravity ____________________ ____________________ ____________________ Hardness _______________________ _______________________ _______________________ Cleavage & Fr acture _______________________ _______________________ _______________________ _______________________ Special Properties ________________________ ________________________ ________________________ ________________________ Minerals are identified based on their physical properties. gold crystals magnetite same size - different densities galena (with silver) diamond mica sulfur Minerals © Copyright NewPath Learning. All Rights Reserved. 94-4101 www.newpathlearning.com Some photos courtesy of USGS. \|xiBAHBDy01790lz[

Minerals

Science, Grade 8

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