Chapter 5 Section 2

1
Chapter 5 Section 2

• Identifying Minerals

2
Physical Properties of Minerals

• Color
• Streak
• Luster
• Cleavage and Fracture

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Color
Amethyst (Variety of Quartz)
Pure Quartz

• Color is an observation.
• Color alone is generally not a reliable clue for
  identifying a mineral sample.
• Many minerals are similar in color.
• Very small amounts of certain elements may
  greatly affect the color of a mineral.
• Weathered surfaces may hide the color of minerals.

Clear Gypsum
4
Streak

• The color of a mineral in powdered form.
• Streak is a test, not an observation.
• Rub some of the mineral against a piece of
  unglazed ceramic tile called a streak plate.
• More reliable then color in identifying minerals.
• The streaks color may differ from the color of
  the solid form of the mineral.

5
Luster

• The way in which a mineral reflects light.
• Metallic luster if the mineral reflects light
  as a polished metal does.
• Nonmetallic luster all other minerals.
• Glassy luster
• Waxy luster
• Pearly luster
• Brilliant luster
• Dull or earthy luster

6
Cleavage and Fracture

• Cleavage in geology, the tendency of a mineral
  to split along specific planes of weakness to
  form smooth, flat surfaces.
• Fracture the manner in which a mineral breaks
  along either curved or irregular surfaces.

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Cleavage

• In a mineral, some bonds may be weaker or
  stronger than others.
• Bond a force (glue) that holds atoms together.
• If a mineral is stressed it will usually break
  along weak bond points.
• Can be identified by looking for flat smooth
  surfaces once the mineral is broken open.
• Crystal form and cleavage are different.
• Crystal form the shape of an unbroken mineral.

8
Fracture

• Three subclasses of fracture
• Uneven or irregular rough surface.
• Splintery or fibrous broken surface that looks
  like a piece of broken wood.
• Conchoidial curved surfaces. How glass
  fractures.