Physical Prosperities of Minerals

o   Primary physical characteristics: crystal form, color, cleavage or fracture, ability to transmit light, luster, streak, hardness

o   Crysal form – external expression of minerals internal structure, crystal growth often interrupted due to competition for space and rapid loss of heat, cant always see crystal form because crystals are too small

o   Luster – the way in which mineral surface reflects light, two basic categories (metallic and non-metallic) ex. galena

o   Color – interaction of light with mineral, obvious feature but often unreliable as a diagnostic property of a particular mineral, gemstones names originated before mineral structure and composition were known, ex. ruby = tiny amounts of chromium, thus red color

o   Streak – color of mineral in its powered form, a plate is used, ex. hematite can be different colors but the streak is always reddish-brown

o   Hardness – resistance to abrasion or scratching, Mohs scale of hardness

o   Cleavage: tendency of mineral to break along plane(s) of weak bonding

o   Cleavage – produces flat, shiny surfaces, number and direction of cleavage planes can be helpful for identification

o   Fracture – many minerals don’t fracture along cleavage surfaces, fractures may be irregular, fibrous, or conchoidal

o   Ability to transmit light – opaque: no light transmits, translucent: light transmits, but no images, transparent: light and images are visible through the mineral

o   Specific gravity: weight of a mineral compared to the weight of an equal volume of water

·       Physical Properties: Secondary

o   Reaction to hydrochloric acid (calcite)

o   Magnetism (ability to be magnetic)

o   Magnetite

o   Double refraction (calcite)

o   Taste (halite)

o   Smell (sulfur)