Mineral Appearance  Individual minerals have unique properties that distinguish them.  Color and appearance are two obvious clues that can be used to identify minerals.  These clues alone are not enough to distinguish most minerals. Pyrite and gold are the same color and can appear similar. You need to look at the other properties to tell them apart.

Hardness  A measure of how easily a mineral can be scratched is called its hardness.  The mineral talc is so soft that you can scratch it with your fingernail. Diamonds are the hardest mineral.  In 1824, Friedrich Mohs developed a list of common minerals to compare their hardness. This list is called the Mohs scale of hardness.  The scale lists the hardness of ten minerals. Talc is the softest and has a hardness value of one. Diamond is the hardest and has a hardness value of ten.

Moh’s Hardness Scale

Luster  Luster is the way a mineral reflects light.  Luster can be metallic or nonmetallic.  Minerals with a metallic luster shine like metal, like gold or graphite.  Minerals with a nonmetallic luster can be described as dull, pearly, silky, or glassy, like quartz and halite.

Luster

Specific Gravity  The specific gravity of a mineral is the ratio of its weight compared with the weight of an equal volume of water.  Specific gravity is expressed as a number.  The specific gravity of gold is 19, which means that gold is 19 times heavier than water.  The specific gravity of pyrite is 5, which means that pyrite is 5 times heavier than water, and that pyrite feels much lighter than an equal-sized sample of gold.

Specific Gravity

Streak  When a mineral is rubbed against a piece of unglazed porcelain tile, a streak of powdered mineral is left behind. Streak is the color of a mineral in its powered form.  The streak test only works for minerals that are softer than the streak plate.  Graphite is used in pencil lead because it is soft enough to leave a streak on paper.

Streak

Cleavage and Fracture  The way a mineral breaks is another clue to its identity  Minerals that break along smooth, flat surfaces have cleavage.  Mica is a mineral that breaks along smooth, flat planes.  Minerals that break with uneven, rough, or jagged surfaces have fracture.  Quartz is a mineral with fracture.

Cleavage

Fracture

Other Properties  Some minerals have unique properties.  Magnetite is attracted to magnets.  Light forms two separate rays when is passes through calcite, causing you to see a double image.  Calcite also fizzes when hydrochloric acid is put on it.

Unique Properties

Taste like salt (Halite)

Smells like eggs (sulfur)

Gems  Gems, or gemstones, are highly prized minerals because they are rare and beautiful.  Most gems are special varieties of a particular mineral. They are clearer, brighter, or more colorful than common samples of that mineral.  In addition to their beauty, some gems serve useful purposes. Because diamonds are so hard, they are useful as cutting tools. Rubies can be used to produce types of laser light and quartz crystals are used in electronic and timepieces.

Ores  A mineral or a rock is an ore if it contains a useful substance that can be mined at a profit.  Iron is obtained from its ore hematite.  Aluminum is refined from the ore bauxite. Smelting is the process by which aluminum oxide powder is converted to aluminum.  Aluminum is made into useful products like bicycles, soft-drink cans, and parts for cars and airplanes.

Vein Minerals  Metallic elements can dissolve in fluids. These fluids can travel through weaknesses in rocks and form mineral deposits.  Mineral deposits left behind that fill in the open spaces created by the weaknesses in rock are called vein mineral deposits.