Identifying Minerals

1
Identifying Minerals

• Geologists rely on several relatively simple
  tests to identify minerals
• These tests are based upon a minerals physical
  and chemical properties

2
Identifying Minerals

• Color
• Many times the color of a mineral is caused by
  the presence of trace elements or compounds.
• One of the least reliable clues to a minerals
  identity
• Example Quartz can be found in a variety of
  colors, including red jasper, purple amethyst,
  and orange citrine.

3
Identifying Minerals

• Luster
• The way a mineral reflects light
• Luster can be either metallic or nonmetallic
• Silver, gold, copper, and galena have shiny
  surfaces that reflect light they are said to
  have a metallic luster
• Nonmetallic minerals such as calcite, gypsum,
  sulfur, and quartz to not shine like metals they
  are described as being dull, pearly, waxy or silky

4
Identifying Minerals

• Texture
• Texture describes how a mineral feels to the
  touch
• The texture of a mineral might be described as
  smooth, rough, ragged, greasy, soapy, or glassy.
• Texture is usually used in combination with other
  tests

5
Identifying Minerals

• Streak
• Streak is the color of a mineral when it is
  broken up and powdered
• A minerals streak does not always match its
  external color
• The mineral is rubbed across an unglazed
  porcelain plate in order to produce a colored
  powdered streak on the surface of the plate

6
Identifying Minerals

• Hardness
• Hardness is a measure of how easily a mineral can
  be scratched
• The Mohs Hardness Scale rates minerals on whether
  they can scratch other minerals.
• Example Diamond is a 10 on the Mohs scale, since
  it cannot be scratched and can scratch all other
  minerals

7
Identifying Minerals

• Cleavage and Fracture
• A mineral that splits relatively easily and
  evenly along one or more flat planes is said to
  have cleavage
• Examples mica breaks in sheets, halite breaks in
  three directions
• Minerals that break with rough or jagged edges
  are said to have fracture
• Examples Flint, obsidian have an arclike
  fracture pattern resembling chain shells

8
Identifying Minerals

• Density and Specific Gravity
• Density is the ratio of mass to volume of a
  substance
• Density reflects the atomic weight and structure
  of a material
• Specific gravity is the ratio of the weight of a
  substance to the weight of an equal volume of
  water at 4 degrees Celsius