How to identify common minerals

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Physical Properties of Minerals

• How to identify common minerals

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What is a mineral?

• A mineral is a naturally occuring, inorganic
  solid with an orderly internal arrangement of
  atoms (called crystalline structure) and a
  definite, but not fixed chemical composition.
• Minerals, especially gems and precious metals,
  are among the oldest objects used an treasured by
  society.
• Example 1 Hematite ? Metal Iron
• Example 2 Gypsum? Drywall

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Optical Properties Luster

• Luster describes the manner in which light is
  reflected from the surface of a mineral
• Any mineral that shines with a metallic-like
  appearance has a metallic luster.
• Those minerals that do note have a metallic
  luster are termed nonmetallic and may have one of
  a variety of lusters which include vitreous,
  pearly, or earthy.

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Example of Luster

• Metallic Luster
• Pyrite, commonly known as fools gold

• Nonmetallic Luster (Earthy)
• Limonite, commonly known as iron ore

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Optical Properties Light Transmission

• Opaque The mineral does not transmit any light.

• Translucent The mineral transmits light, but not
  an image.

• Transparent An image is visible through the
  mineral.

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Hardness The Mohs Scale

• Hardness, one of the most useful diagnostic
  properties of a mineral, is a measure of the
  resistance of a mineral to abrasion or
  scratching.
• A harder substance with scratch or cut into a
  softer substance.
• The Mohs scale, developed by the German
  mineralogist Friedrich Mohs, rates mineral
  hardness on a 10 point scale.
• 1 softest mineral in the set
• 10 hardest mineral in the set

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Streak

• The streak of a mineral is the color of fine
  powder of a mineral obtained by rubbing a corner
  across a piece of unglazed porcelain called a
  streak plate.
• The streak of a mineral is unique to the mineral
  where the color of a mineral may vary.

• Hematite (left) may look black, but it will
  always produce a RED/BROWN streak on a streak
  plate.
• Pyrite (right)looks yellow-gold in the crystal
  form, but gives a GRAY streak when the plate is
  used.

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Crystal Form

• Crystal form is the external appearance or shape
  of a mineral that results from the internal,
  orderly arrangement of atoms.
• In nature, minerals must compete for space and
  the result is a dense intergrown mass in which
  crystals do not exhibit their crystal form.

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Cleavage and Fracture

• Cleavage is the tendency of some minerals to
  break along regular planes of weak bonding
  between atoms in the internal crystalline
  structure.
• When a mineral is broken the flat smooth surfaces
  of the mineral are called cleavage planes.
• Cleavage is determined by noting the number of
  directions of cleavage and the angles at which
  the directions of cleavage meet.

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• Minerals that do not exhibit cleavage when broken
  are said to fracture.
• Fracturing can be irregular, splintery or
  conchoidal .

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Other Properties of Minerals

• Magnetism- magnetite (lodestone)
• Taste- halite has a salty taste
• Feel- talc has a soapy feel while graphite
  feels greasy
• Striations- feldspar minerals
• Reactions to dilute Hydrochloric Acid- carbonate
  minerals effervesce due to the release of carbon
  dioxide