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WHAT IS A MINERAL? Earth Science Chapter 4 Section 1 Mineral Characteristics Mineral Naturally occurring Inorganic Solid Specific chemical composition Definite crystalline structure Rock Forming Minerals 3000 minerals occur in Earth’s crust 8-10 refered to rock forming minerals Make up most of the rocks Minerals from Magma Magma less dense than surrounding rocks As cools, crystals form Elements in magma determine the mineral formed Large crystals Rises Cool slowly, atoms have time to arrange in large crystals Small crystals Rapidly cooling magma Minerals from Solution Minerals dissolved in water Salts Saturated Water can’t hold any more of the substance Supersaturated - Precipitates Solution becomes overfilled Conditions right for minerals to form Individual atoms bond together and mineral crystals form into solids from the solution Minerals form Solutions Evaporates Minerals crystallize when the solution evaporates Crystal Form Distinct crystal shape Easily recognizable Halite- cubes Quartz - double pointed ends Perfect crystals are not the norm Crystallization should not be used as only form of identification Luster Metallic Luster Metallic luster Shiny surfaces that reflect a lot of light Non Metallic Luster Nonmetallic luster Do not shine Dull, pearly, waxy, silky or earthy Hardness Hardness is the measure of how easily a mineral can be scratched. Most useful and reliable of all tests Mohs Hardness Scale used to compare minerals Cleavage and Fracture Cleavage A mineral that splits easily alone one or more flat planes Fracture Minerals that bread with rough jagged edges Conchoidal fracture Streak The powder left on a ceramic plate when a mineral is scratched along it. Does not always match the color of the mineral. Color Most noticeable characteristic Least reliable Sometimes caused by trace elements or compounds within the mineral Special Properties Magnetism Striations Double refraction Light Effervescence Does is split into two rays if fizz? Fluorescence Shine in ultraviolet light Texture How the mineral feels to the touch Subjective Used with a combination of tests Specific Gravity Ratio of the weight of the mineral with the weight of an equal volume of water. Specific gravity of minerals can be roughly relatively tested using heft.
