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Chapter 2: Properties of Minerals (2.3). 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

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minerals the building blocks of rocks
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
How do we identify minerals?
  • Physical properties:
    • Color
    • Streak
    • Luster
    • Hardness
    • Crystal form
    • Cleavage
    • Fracture
    • Density
    • Distinctive
physical properties of minerals
Physical Properties of Minerals
  • Color:
    • Most obvious, but often misleading
    • Different colors may result from impurities

Example:

Quartz

physical properties of minerals1
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 minerals2
Physical Properties of Minerals
  • Luster:
    • How a mineral surface reflects light
    • Two major types:
      • Metallic luster
      • Non-metallic luster

Metallic

example:

Galena

Non-metallic

example:

Orthoclase

physical properties of minerals3
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)
slide8

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)

Mohs Scale of Hardness

physical properties of minerals4
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

Pyrite

Quartz

physical properties of minerals5
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 minerals6
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 minerals7
Physical Properties of Minerals
  • Cleavage (1 direction):

Example: mica

physical properties of minerals8
Physical Properties of Minerals
  • Cleavage (2 directions):

orthoclase

amphibole

physical properties of minerals9
Physical Properties of Minerals
  • Cleavage (3 directions):

halite

calcite

physical properties of minerals10
Physical Properties of Minerals
  • Cleavage (4 directions):

fluorite

physical properties of minerals11
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 minerals12
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

D=7.5

Quartz

D=2.65

physical properties of minerals13
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)