2. What is a Mineral?
Mineral: inorganic solid material found in nature
•Same chemical makeup
•Orderly pattern of atoms
•Building blocks of all rocks
•Over 4000 minerals identified
•Form from melted rock or
from solutions that evaporate
Fluorite
3. How Minerals Form
•We can get a clue how a mineral formed by how it looks…
•Look at size of grain or crystal
•presence of layers, texture
•the way mineral grains fit together
•like a puzzle- cooled from magma
•layers of different minerals- probably formed by evaporation
4. Cooled From Magma
There are two main ways
that new crystals of
minerals grow. Some
minerals form when
molten rock, called magma
below the planet’s surface
and lava above, cools and
atoms bond together into
mineral crystals.
5. Minerals from Evaporation
Other minerals form when water that has atoms of dissolved elements in it,
evaporates away. The atoms get very close to each other and may bond
together to form solid minerals.
When ancient seas slowly evaporated, minerals like halite, gypsum, and
calcite formed.
Halite Gypsum Calcite
6. Properties of Minerals
Properties can be used to help identify minerals…
1) Crystals
2) Cleavage/Fracture
3) Streak
4) Luster
5) Hardness
6) Other Properties
7. 1) Crystals
1) Crystals- atoms of minerals are arranged in repeating
patterns
• Smooth surfaces
• Sharp edges
• Points
8. 2)2) Cleavage / FractureCleavage / Fracture
Can study the way mineral breaks…
•Splits with smooth, regular edges
and surfaces- said to have cleavage
(ex- mica)
Βreaks into pieces with jagged/rough edges
(ex- quartz, native copper)- said to fracture
9. 3) Streak
Color can fool you (ex- pyrite)
Streak test will help identify even if
It looks like a different mineral
Scratching mineral sample across
unglazed white tile (streak plate)
produces streak of color
(not always same as mineral itself in color)
Pyrite- greenish-black or brownish-black streak
Gold- yellow streak
10. 4) Luster
Luster- how light is reflected from
mineral’s surface
•Shines like mineral- metallic luster
•Nonmetallic minerals- pearly,
glassy, dull, earthy luster
13. Mineral Luster Glassy
Many samples with non-metallic luster are shiny, but it is the
shine of glass rather than metal.
Calcite
Garnet
Aragonite
Amethyst
14. Mineral Luster Dull or Earthy
Earthy luster is applied to samples that look powdery or soil-
like.
KaoliniteLimonite Chrysocolla
15. 5) Hardness
1822- Austrian Friedrich Mohs developed
Mohs scale- way to classify minerals
from 1 (softest) to 10 (hardest)
You can use a penny, nail, or
glass plate with smooth
edges to test hardness.
Can the mineral scratch a
penny? Glass?
16. 6) Other Properties
• Magnetism (ex- magnetite)
• Calcite- fizzes when in contact with an acid like
vinegar
• Fluorite glows under ultraviolet light
• Halite or rock salt tastes salty
• Sulfur has an unusual odor
Calcite in vinegar
17. Common Minerals
In rocks, the most common minerals are:
1. Quartz
2. Feldspar
3. Biotite
4. Mica
5. Calcite
6. Gypsum
7. Hornblende
8. Fluorite
9. Augite
10. Hematite
1
2
3
4
5
6
7
8
9
10
18. Gems
Most other minerals (diamonds, emeralds, etc.) are rare
Gems: minerals that are rare and can be cut and
polished, giving a beautiful appearance
– Must be clear with no blemishes/cracks
– Must have a beautiful color
19. Ores
Ores: a mineral that contains something that can be useful
and sold for profit
– Many metals come from ore
– Iron: comes from mineral hematite
– Lead (for batteries): produced from galena
– Magnesium (in vitamins): comes from dolomite
Notes de l'éditeur
Rocks are usually made of 2 or more minerals
Cleavage- caused by weaknesses in arrangement of atoms that make up mineral
Pyrite is shiny, gold color- like real gold… fooled miners in Gold Rush days (1800s). Called fool’s gold
A gold nugget and its golden streak are at the upper right. A pyrite crystal and its black streak are at the lower left.
Talc- scratched with fingernail
Diamond- so hard, can cut almost anything else
A 4 (fluorite) will scratch a 3 (calcite)
