Earth Minerals
Earth Minerals
Minerals
• Crystalline solid• Pure substance• Found in nature• Inorganic
Rocks
• Solid aggregate of minerals (mixtures)
Physical Properties
• Color• Luster• Cleavage• Hardness• Streak• Crystal Form• Specific Gravity• Special Properties
Color
• Most obvious characteristic of minerals
• Most unreliable characteristic for identifying minerals
• Impurities cause color variations• Example: Quartz
Luster
• Appearance or quality of light reflected from the surface of the mineral
• Descriptions:Metallic – look like metal regardless of color
Cleavage
• A minerals tendency to break along flat surfaces– Depends on the type of bond used
during the formation of mineral
• Fracture – minerals that break unevenly into curved or irregular pieces
• How to test: break the mineral
Hardness• Measure of minerals ability to resist
scratching• Does not mean resistance to cleavage or
fracture• Hardest mineral – diamond• Hardest common mineral – quartz• Softest common mineral - talc• How to test – rub mineral along a glass
slide to see if it scratches the glass or not
Streak• Color of a mineral in its powdered
form• More reliable indication of mineral
color• How to test: rub mineral against
streak plate
Crystal Form• External
expression of a mineral’s internal orderly arrangement of atoms
• How crystals will grow without interference
Specific Gravity• How dense a mineral is compared to
water• Minerals denser than water have a
density greater than 1– Quartz, feldspar, calcite, and talc – 3
specific gravity– Hematite and magnetite – 5 specific
gravity– Gold – specific gravity – 19.3 when pure
• Minerals less dense than water have a density below 1
Specific gravity…
weight of sample in air
loss of weight in waterSpecific gravity =
Special Properties
• Magnetic –– Magnetite – most common magnetic
mineral– Lodestone – type of magnetite that acts
like a magnet
• Fizzes with acid:– Calcite will fizz when hydrochloric acid is
placed on the sample– The fizz produces carbon dioxide gas
CO2
• Taste:– Mineral will have a particular taste like
salt– How do you test – lick it
• Fluorescence– Minerals absorb ultraviolet light and then
produce visible light of various colors– Calcite appears white but under UV light
appears red
• Odor – – Minerals that
smell– Sphalerite – rich
in zinc– How to test –
scratch the mineral and smell
• Double Refraction – – Light rays that bend as they pass
through the mineral– When the light bends it splits into 2 rays
and produces a double image
Mineral ID practice…What is…?1.
2.
3.
How Crystalline Minerals Form
• Evaporation of solutions– Halite and Gypsum
• Cooling of melted substances– Quartz and Olivine