Post on 21-Jan-2016
Mineral IdentificationAim: How do we identify minerals?
Chapter 3: section 2
REVIEW: WHAT IS A PHYSICAL PROPERTY?
A physical property is any characteristic of a material that you can observe without changing the identity of the material.
Example: How would you distinguish pyrite (fool’s gold) from gold?
MINERAL APPEARANCE
Color Appearance
Example: Pyrite and fool’s gold are both gold in color. Gold is worth a lot of money. Pyrite has little value.
HARDNESS
Hardness is the measure of how easily a mineral can be scratched. The mineral talc is so soft you can scratch it
with your fingernail. This is the softest mineral. Diamonds are the hardest mineral.
Example: gold – hardness 2.5 - 3 pyrite – hardness 6 - 6.5
(***Do not confuse hardness with how a mineral can break***)
MOHS SCALE Friedrich Mohs
developed a list of common minerals to compare their hardnesses.
This list is called Mohs scale of hardness.
MOHS SCALE
Some minerals have a hardness range rather than a single hardness value. This is because atoms are arranged differently in different directions in their crystal structures.
LUSTER A way a mineral
reflects light is known as luster.
Luster may be metallic or nonmetallic.
Metallic – shines like a metal
Nonmetallic – glassy, dull, pearly, silky
SPECIFIC GRAVITY
Minerals can be compared by comparing the weights of equal-sized samples.
The specific gravity of a mineral is the ratio of its weight compared with the weight of an equal volume of water.
Example: Gold is 19 times heavier than water. Pyrite is 5 times heavier then water.
The tern heft describes how heavy a mineral sample feels.
STREAK When a mineral is rubbed across a piece of
unglazed porcelain tile, a streak of powdered mineral is left behind.
Streak is the color of a mineral when it is in a powdered form.
The streak test only works for minerals that are softer than the streak plate.
Example: Gold – yellow streakPyrite – greenish-black/ brownish-black streak
CLEAVAGE AND FRACTURE
Minerals that break along smooth, flat surfaces have cleavage. Cleavage like hardness is determined
partly by the arrangement of a minerals atoms.
Minerals that break with uneven, rough, or jagged surfaces have fracture.
OTHER PROPERTIES
Some minerals may have unique properties.
Magnetite – attracted to magnets