Lab 4 - Minerals
•
Minerals
1. Inorganic
2. Naturally occurring
3. Have characteristic
chemical composition
- Crystalline structure
(orderly 3D
arrangement of
atoms/molecules)
•
Rocks - Aggregates of
1+ mineral(s)
Mineral Properties
1. Color and Clarity
-
Color
Clarity
-
Transparent = seethrough
Translucent = foggy
Opaque = can’t see
through
Mineral Properties
2. Crystal Form
(Habit)
-
Geometric shape of
the crystal
-
-
-
Cubes, pyramids,
prisms, etc.
Perfect crystal habit
= only occurs when
crystal has room to
grow (rare)
Different from
cleavage  way
the crystal grows,
not the way it
breaks!
Mineral Properties
3. Luster
-
How light reflects off an
object
Types:
-
Metallic luster (M)
Non-metallic luster (NM)
-
Vitreous
Waxy
Pearly
Satiny
Earthy
Greasy
Porcelaneous
Mineral Properties
4. Hardness
-
Measure of mineral’s resistance
to scratching.
Mohs Scale of Hardness
-
-
Quantitative scale of relative mineral
hardness
1 = talc (softest mineral)
10 = diamond (hardest mineral)
Hardness of common objects:
- Fingernail = 2.5
- Penny = 3.5
- Nail = 4.5
- Glass = 5.5-6
- Streak plate = 6.5
Mineral Properties
5. Streak
-
-
Streak = the powder that remains when
you scratch something against the
streak plate
Minerals harder than 6.5 do not leave
their streak
-
-
powder left behind = powder of streak plate
Usually same for the same mineral 
even with different varieties of that
mineral
Crystal form
Mineral Properties
Cleavage
6. Cleavage and Fractures
-
Cleavage = breaks along
flat, parallel surface
Cleavage planes = parallel
surfaces of weak chemical
bonding
-
-
-
-
May be one or more
Cleavage direction =
orientation of each set of
cleavage plane
Fracture = break in a
mineral not along a
cleavage plane
Mineral Properties
6. Cleavage and
Fractures
-
Cleavage direction
may be:
-
-
Excellent, Good, Poor
Types:
–
–
–
–
–
–
–
Basal (mica)
Cubic (halite)
Octahedral (fluorite)
Dodecahedral (garnet)
Rhombohedral (calcite)
Prismatic
Conchoidal – ribbed, smoothly
curved surfaces (like glass)
Mineral Properties
7. Other properties
-
Reaction to acid – mineral fizzes
when weak HCl is added
- Carbonate minerals
-
Striations – straight, hairline grooves
on the cleavage surface.
- Feldspars
-
Magnetism – attracted to magnets
-
Specific gravity – ratio of the density
of a substance divided by the
density of water
- How heavy is it?
Notes on today’s lab
• BEWARE OF COLOR!
– The same mineral can be many different colors
– Different minerals can be the same color
• Identify consistently
• Only write what you can see, don’t copy the
book’s descriptions
• 16 minerals, multiples for some
– Minerals you will identify are all on your lab
handout