8 - Unit 1, Section 3 - Day 1

If you had to identify a mineral just by observing it, what properties would you use?

Popcorn Activity

Mineralogists (scientists who study minerals) can identify them based on the following physical properties:

• Color

• Luster

• Streak

• Hardness

• Cleavage

• Fracture

• Density

Useful Properties of Minerals

• Some minerals have a characteristic color that can be used to identify them

• Chemical impurities in minerals cause also different colors

• Color alone cannot be used to identify a mineral

Color

Luster - the way a mineral reflects or absorbs light at its surface

• Minerals can have:

  • Metallic luster - the mineral reflects the most light

  • Shiny luster - reflects light, but not as much as metals

  • Dull luster - absorbs more light than it reflects

Luster

Streak - the color of a mineral in powdered form

• Caused by rubbing a mineral against an unglazed porcelain plate

Streak

Hardness - the resistance of a mineral to being scratched

• The Mohs Scale is used to compare the hardness of different minerals

• The Mohs Scale ranges from 1 (the softest) to 10 (the hardest)

Hardness

The Mohs Scale

• Cleavage - the ability of a mineral to break into smooth, flat surfaces

• Fracture - the breakage of a mineral into uneven surfaces

Cleavage and Fracture

Density

• Texture - some may feel greasy (graphite) or smooth (talc)

• Chemical Reaction - calcite fizzes and dissolved when exposed to hydrochloric acid

• Odor - sulfur smells like a burnt match

• Fluorescence - some minerals glow when exposed to ultraviolet light

• Magnetism - magnetite is magnetic due to iron

Special Properties