UNIT 2 MINERALS PART 2 full lecture
Structure of minerals
Composition of magma or fluids from which the
minerals form.
Conditions like temperature and pressure under
which the mineral forms.
Minerals formed from the same elements in the
same proportions can have very different internal
structures, (ex)depending on pressure which packs
atoms more dense.
• 1. Polymorphs- different minerals with the same
chemical composition but differing structures.
• Graphite is a form of pure carbon.
• Its crystal structure forms sheets
• of carbon
Diamond is another form of pure
carbon. It forms deep in the Earth
at high pressures and it’s the
hardest substance.
It crystal structure is dense and
compact.
• 2. Mineral Identification
• Minerals are identified by their physical and
optical properties. Some properties are more
diagnostic then others so a combination is used
to determine the mineral.
• Properties: color, luster, hardness, streak, Crystal
form, cleavage, fracture, reaction to acid, taste,
smell, magnetization, optical properties,
elasticity, and specific gravity.
• a. Color can be misleading, some impurities in the
mineral can change its color.
• b. Luster appearance of light reflected from
minerals. Eamples include metallic luster,
nonmetallic luster, glassy luster, and resinous
luster.
c. Hardness measures minerals resistance to
scratching.
Mah’s hardness scale.
d. Crystal form reflects internal arrangement of atoms
The shape of a well-formed crystals reflects light by
arrangement of atoms.
Anhedral crystals form when
crystals don’t have room
to grow and bump into each other
feldspar in an igneous rock
Irregular boundaries between crystals
due to interference during growth
Anhedral crystals
formed by crowding
during growth
Quartz geode
Crystal terminations of
euhedral quartz
Anhedral quartz crystals
formed by crowding
during growth
Euhedral crystals of amphibole in a volcanic rock
Asbestos
Asbestos
-group of silicate minerals that readily separate into fibers
that are: thin, flexible, heat resistant, chemically inert
many uses
Cleavage: Tendency to break along
preferred planes of weakness.
Cleavages represent directions of
weaker bonding between atoms.
Conchoidal fracture
in volcanic glass
Streak: Color of mineral
in its powdered form
Hematite: Iron oxide
Carbonate minerals, like calcite, dissolve
in acid and release carbon dioxide
“The Acid Test”
CO2 bubbles
Important Non-silicate Minerals
Halides
Halite (Na, Cl: NaCl)
-> common table salt
Sulfates
Gypsum (Ca,S,O,H: CaSO4-H2O)
-> calcium sulfate + water, main ingredient of
plaster & other building materials
Oxides
Hematite (Fe, O: Fe2O3)
-> steel
Important Non-silicate Minerals
Carbonates
Calcite (Ca, C, O: CaCO3)
Dolomite (Ca, Mg,C, O: CaMg(CO3)2
 Found together in sedimentary rock limestone.
 Main ingredient to cement, roads & building stones.
The Common Rock-forming Minerals
Over 4000 minerals: only few dozen are abundant, making up
most rocks of Earth’s crust
=> rock-forming minerals
Only 8 elements make up most of crust’s minerals & represent
over 98% of the continental crust
The two most abundant elements:
 Silicon (Si)
 Oxygen (O)
Question: What minerals would
you expect to be most abundant on Earth?
Percent of elements by WEIGHT
Average composition of the Earth’s crust.
The Common Rock-forming Minerals
Earth’s Crust
Primarily Si & O followed in abundance by
Fe, Mg, Ca, Na, K, etc.
Dark colored (mantle and oceanic crust)
Olivine (Si, O, Fe, Mg)
Pyroxene (Si, O, Fe, Mg, Ca)
Amphibole (Si, O, Fe, Mg)
Light colored (crust, esp. continental crust)
Quartz (SiO2) - Hard, transparent
Feldspar (Si, O, Al, K, Na, Ca) - Hard, white, gray, pink
Clay (Mostly come from weathering feldspar)
Calcite (CaCO3, shells) Limestone - Used for cement