W3.2 Minerals
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How are minerals identified?
Using characteristics detected by our senses - sight, smell, touch, taste
Define “diagnostic features”
Some mineral properties are distinctive and help differentiate similar-looking minerals
What are 8 common physical properties? (FRSH LCCS)
• Fracture or cleavage • Reaction to acid • Specific gravity (density) • Hardness • Luster • Colour • Crystal habit • Streak
What is the colour of a mineral determined by?
The wavelengths of light that the crystal reflects or refracts
What causes variation in mineral colour?
Trace impurities in crystal lattice
Give examples of 2 minerals for which colour is diagnostic
• Olivine (olive green mainly due to iron) • Azurite (deep blue due to copper)
What is streak?
The colour of a mineral in powdered form, typically tested by rubbing it on an unglazed ceramic plate
What is the difference between congruent and incongruent streak?
Congruent streak - streak colour same as mineral Incongruent streak - streak colour different than mineral
What is luster? What are its two subdivisions?
The way a mineral scatters light; metallic and nonmetallic
What are the subdivisions of nonmetallic luster? (VAPERSS)
Vitreous (glassy) Adamantine (brilliant) Pearly Earthy (dull) Resinous Satiny Silky
Define hardness; what does it reflect?
A mineral’s resistance to scratching; mainly reflects bond strength
What is Freidrich Moh’s scale of hardness? (Tall Gyrating Cattle Feed All Our Queen’s Top Court Dudes)
Talc Gypsum Calcite Fluorite Apatite Orthoclase Quartz Topaz Corundum Diamond
Define crystal habit
Overall external shape of a single crystal or a group of crystals that grew together
What determines crystal habit? What are 3 types of directional rates? (3,2,1)
• Habit is determined by atomic arrangement and growth rates in different directions Three types of directional rates: 1. Blocky or equant – equal growth rate in three dimensions (pyrite, garnet) 2. Bladed – rapid growth in two dimensions (shaped like a knife blade) (kyanite) 3. Needle-like – rapid growth in one dimension, slow in others (crocoite)
How do minerals with equal bond strength break?
By fracturing rather than cleaving
What is cleaving? What does it produce and what is it described by?
The tendency of a mineral to break along planes of weaker atomic bonds, producing flat shiny surface; it is described by the number of planes and their angles
How do cleavage and crystal habit/faces differ?
Cleavage is throughgoing, often forming parallel steps; crystal faces only occur on external structures
What is effervescence?
Reactivity with acid
What is magnetism?
magnetic attraction
What is elasticity?
response to bending
What is diaphaneity?
relative transparency
What is piezoelectricity?
electric charge when squeezed
What is refractive index?
degree of bending light
What is sectility?
ability to be cut with a knife