Identifying Minerals Properties: Color, Luster, Streak, Density, Hardness, Cleavage, Fracture, and Special Properties
Color The same mineral can come in a variety of colors Ex. quartz Impurities & other factors can change mineral appearance Color is not the best way to identify minerals
Luster Describes how a surface reflects light Ex. shiny/dull Metallic- minerals containing metals are often shiny
Luster Examples of Nonmetallic Nonmetallic- not as shiny Vitreous- glassy, brilliant Silky-fibrous Resinous-plastic Waxy- greasy, oily Pearly- creamy Earthy- rough, dull Nonmetallic- not as shiny
Streak Color of mineral in powder form Observed by rubbing a mineral against a piece of unglazed porcelain called a streak plate Streak doesn’t vary like color & is often different than a mineral’s color More reliable than color
Cleavage and Fracture
Cleavage and Fracture- ways the mineral breaks apart, determined by arrangement of atoms.
Hardness Minerals resistance to being scratched Mohs’ Hardness Scale: Ranks minerals from softest to hardest Talc- softest known mineral Diamond- hardest known mineral
Hardness
Mohs Hardness Scale Talc 1 Softest known mineral Gypsum 2 fingernail can scratch it Calcite 3 scratched by copper penny Fluorite 4 easily scratched by steel knife Apatite 5 can be scratched by steel knife Orthoclase 6 can scratch window glass Quartz 7 can scratch steel Topaz 8 can scratch quartz Corundum 9 can scratch topaz Diamond 10 hardest known mineral
Density mass (how heavy it is) per unit volume (how much space it takes up) D= M/V Density remains same regardless of sample size Mass determined using balance Volume determined using water displacement method. Ex: gold is heavier than pyrite (fools gold)