You can use different properties of minerals to help identify them Color Luster Streak Cleavage & Fracture Hardness Density Other Special Properties

Color Same mineral can exist in a variety of colors Pure quartz Black Onyx quartz Rose quartz Purple Amethyst Yellow quartz Smokey Brown

Color Various amounts and types of impurities affect color Impurities like other minerals Exposure to other substances (air, water, etc.) Not usually the best way to identify a mineral

Luster The way a surface reflects light “shiny or dull” Minerals Classified as 1) metallic luster bright, “shiny”, reflective gold galena 2) sub-metallic luster dull, reflective hematite

Luster 3) nonmetallic luster (see Section 2 Figure 1) Vitreous Silky Resinous Waxy Pearly Earthy

Streak The color of a mineral in its powdered form Found by rubbing the mineral against a streak plate (unglazed porcelain) Not always the same color as the mineral sample Not affected by air More reliable than using color in identification

Cleavage & Fracture The way a mineral breaks/fractures is determined by the arrangement of its atoms Cleavage-the tendency of some minerals to break along smooth, flat surfaces Fracture-the tendency of some minerals to break unevenly along curved or irregular surfaces

Hardness A minerals resistance to being scratched Mohs Hardness Scale uses 10 reference minerals for comparison If the reference mineral scratches your unknown, the reference mineral is harder than your unknown

Density A measure of how much matter is present in a given space (D = m/V) Usually measured in g/cm 3 (for solids) Specific Gravity – comparison of object’s density to that of water (which is 1 g/cm 3 )

Special Properties (particular to a few types of minerals) Fluorescence Glow under ultraviolet light Magnetism Attract iron Chemical Reaction “Fizz” (gas released) when weak acid is added Taste Halite has salty taste Optical Properties Calcite and double image Radioactivity Radiation detected with a Geiger counter

The Standard Deviants: Physical Properties for Classifying Minerals