IDENTIFYING MINERALS

Mineral Identification  Geologist test physical and chemical properties to identify minerals  Color  Luster  Texture  Streak  Hardness  Cleavage and Fracture  Density and Specific Gravity  Special Properties

Color  A mineral’s color is a result of chemical composition and presence of trace elements  Many minerals can be found in more than one color or shade  Example – Quartz can be found in several different forms

Jasper  Has traces of iron oxides giving it a red tinge

Amethyst  Contains ferric iron making it purple

Citrine  Contains iron hydrates making them orange

Rose Quartz  Contains manganese or titanium  Color is the most obvious characteristic of a mineral but it is also the least reliable.

Luster  How the surface of a mineral reflects light  Two main categories  Metallic – mineral shines like chrome  Nonmetallic – minerals do not shine More specific type of nonmetallic Dull Pearly Waxy Silky

Texture  How a mineral feels to the touch  Smooth  Rough  Ragged  Greasy  Soapy  Glassy  Texture test is perhaps the most subjective

Streak  The color of the mineral in powder form  Tested by rubbing the mineral across an unglazed  Streak color is not always the same as the mineral color in rock form  Example – pyrite is gold in rock form but has a greenish-black streak

Streak cont.  Different variations of a mineral have the same streak  Example – Flourite can be purple, yellow, green, or blue but the streak is always white  When can this test not be used?  When the minerals are harder than a porcelain plate

Hardness  A measure of how easily a mineral can be scratched.  Measured on the Moh’s Hardness Scale  One of the best identification tests  1-10 scale: Talc is the softest, diamond is the hardest  Common objects can be used to measure hardness

MineralMoh’s Scale Hardness Hardness of Common Object Talc1 (softest) Gypsum2Fingernail (2.5) Calcite3Piece of copper (3.5) Flourite4Iron nail (4.5) Apatite5Glass (5.5) Feldspar6Steel file (6.5) Quartz7Streak plate (7) Topaz8Scratches quartz Corundum9Scratches topaz Diamond10 (Hardest)Scratches all common materials

Cleavage and Fracture  Both describe how a mineral breaks  Cleavage – splits easily and evenly along flat planes Mica  Fracture – breaks with rough, jagged edges Quartz

Density and Specific Gravity  Density  Very good identification tool  Mass divided by volume  Density is different than weight Consider two different amounts of the same mineral Their weights would be different Their densities would be equal  Specific Gravity  Ratio of the weight of a substance to the weight of an equal volume of water at 4° C

Special Properties  Some minerals have unique physical and chemical properties  Double Refraction – light bends in two directions when it passes through the mineral  Magnetism – mineral is naturally magnetic magnetite  Odor – sulfide produces a rotten-egg smell when rubbed on streak plate  Fizzes – chemical reaction to acid or other solutions Calcite and hydrochloric acid  Taste

ORES AND GEMS

Ores  A useful mineral can be mined for a profit  Examples  Hematite – source of iron  Bauxite – source of aluminum  Rutile – source of titanium

Gems  Are nothing more than minerals that are valuable simply because they are prized for their rarity and beauty  Examples – Diamonds, Rubies, Amethyst