Minerals: Physical Properties PDF

Physical Properties of Minerals....................................................................................0................................................................................... HOW TO I D E N T I F Y C O M M O N M I N E R A L S Mineral...

Physical Properties of Minerals....................................................................................0................................................................................... HOW TO I D E N T I F Y C O M M O N M I N E R A L S Minerals: the building blocks of rocks Definition of a Mineral: ✓ Naturally occurring ✓ Inorganic ✓ Solid ✓ Characteristic crystalline structure ✓ Definite chemical composition How do we identify minerals? Physical properties: ✓ Color ✓ Streak ✓ Luster ✓ Hardness ✓ Crystal form ✓ Cleavage ✓ Fracture ✓ Density ✓ Distinctive Physical Properties of Minerals Color: Most obvious, but often misleading Different colors may result from impurities Example: Quartz Physical Properties of Minerals Color: Streak – color of a mineral in powdered form (used for metallic minerals) Obtained by scratching a mineral on a piece of unglazed porcelain. Example: Hematite Physical Properties of Minerals Luster: How a mineral surface reflects light Two major types: Metallic luster Non-metallic luster Metallic Non-metallic example: example: Galena Orthoclase Physical Properties of Minerals Hardness: How easy it is to scratch a mineral Mohs Scale of Hardness relative scale consists of 10 minerals, ranked 1 (softest) to 10 (hardest) Mohs Scale of Hardness Hardest (10) – Diamond Softest (1) – Talc Common objects: - Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5) Physical Properties of Minerals Crystal Form (or shape): external expression of a mineral’s internal atomic structure planar surfaces are called crystal faces angles between crystal faces are constant for any particular mineral Quartz Pyrite Physical Properties of Minerals Cleavage vs. Fracture: The way a mineral breaks – Cleavage: tendency of a mineral to break along planes of weakness – Minerals that do not exhibit cleavage are said to fracture Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken. Physical Properties of Minerals Cleavage is described by: Number of planes Angles between adjacent planes – These are constant for a particular mineral Physical Properties of Minerals Cleavage (1 direction): Example: mica Physical Properties of Minerals Cleavage (2 directions): orthoclase amphibole Physical Properties of Minerals Cleavage (3 directions): halite calcite Physical Properties of Minerals Cleavage (4 directions): fluorite Physical Properties of Minerals Fracture: minerals that do not exhibit cleavage are said to fracture – smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture Quartz Physical Properties of Minerals Density: mass of a mineral divided by volume of the mineral metallic minerals tend to have higher densities than non-metallic minerals Galena Quartz D=7.5 D=2.65 Physical Properties of Minerals Distinctive properties: – reaction with hydrochloric acid (calcite fizzes) – taste (halite tastes salty) – feel (talc feels soapy, graphite feels greasy) – magnetism (magnetite attracts a magnet) – double refraction (calcite when placed over printed material, letters appear doubled) – smell (sulfur smells like rotten eggs) Q&A