Properties of Minerals
How to Identify and Classify Minerals
Ways to Identify Minerals
• There are 8 important characteristics for
identifying minerals:
• Color
• Luster
• Hardness
• Streak
• Crystal Form
• Breakage
• Specific Gravity
• Other Special Properties
Color
• It is not the best identification
property.
• Most minerals come in a wide range of
colors.
• Quartz can be: yellow, clear, white, pink,
or purple, etc.
• A few minerals do have specific colors.
• Olivine is always green
Luster
• Luster- the way light reflects off of a
mineral’s surface.
• Luster is related to color.
• Luster falls into 2 categories
• Metallic
• Makes the mineral look like metal.
• Shiny silver or gold
• Nonmetallic
• Glassy, earthy (dull brown/white),
pearly, resinous (looks like plastic)
Hardness
• Hardness-resistance to scratching.
• Use the MOHS hardness scale.
• Goes from 1-10, where 1 is very soft, and 10 is very hard.
• Can measure hardness using:
•
•
•
•
Fingernail (2.5)
Penny (3.5)
Nail (5.5)
Streak plate (6.5)
Streak
• Streak- the color of powdered material
when it dragged across a streak plate.
• Not all minerals leave a streak.
• Even though the color may vary in
particular minerals, the color of the
streak is unique to each mineral.
• Hematite can be silver, red, brown, or
black. But the streak it leaves is always a
reddish-brown.
Crystal Form
• Crystal Form- external expression of
internal structure.
• You can see the structure of the crystals of
the mineral.
• Good for identification because the size
of the crystals and how they break up
can be a unique feature.
• Some can have multiple crystal forms.
Breakage (Fracture vs. Cleavage)
• Fracture- mineral will break into
uneven surfaces if force is applied.
• The mineral breaks how glass does.
• Cleavage- tendency of a mineral to
break along planes of weak bonds.
• Breaks along a particular plane,
creates smooth parallel surfaces.
• Examples: Halite, calcite, orthoclase.
Specific Gravity
• Specific Gravity- the ratio of
mineral mass to mass of an equal
volume of water.
• How heavy the mineral feels.
• The values defines the mineral.
• Metallic minerals have a higher
specific gravity than more powdery
minerals.
Gild- a mineral with one of the
highest specific gravities.
Special Properties
• Magnetism
• Magnetite is a mineral that is magnetic
• Taste
• Halite (salt) tastes salty
• Reaction to hydrochloric acid (HCl)
• Calcite bubbles when acid is applied
• Smell
• Sphalerite (contains sulfur) smells like
rotten eggs
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