Minerals

MINERALS

Rocks
 What is a rock?
 A rock is a naturally formed
aggregate composed of one
or more minerals

rock, an aggregate of more than one minerals

What is a Mineral?
 A mineral is a naturally formed inorganic crystalline solid
with a definite chemical composition and identifying
physical properties
 naturally formed
 formed by geologic processes in nature, not by humans

 inorganic
 was never alive

 crystalline solid
 a solid composed of atoms arranged in a repeating orderly
framework

 definite chemical composition
 a homogeneous chemical compound with a chemical formula

 distinctive, identifying physical properties

The stuff that makes up all
matter
• The make-up of solid matter on Earth:
Atoms  Elements  Compounds  Minerals  Rocks
(smallest)

• Elements:
– fundamental building blocks
– smallest matter that can’t be broken down

(largest)

Physical Properties of Minerals
1. Crystal form
 Is a set of crystalline faces having a definite
geometric relationship to one another

Garnet

Quartz

Physical Properties of Minerals
2. Color
 Is due to visible wavelengths of light not absorbed
 Is the most obvious but least reliable property to use
for identification
Milky quartz
Citrine

Colors of ruby and sapphire,
varieties of corundum (Al2O3)

Amethyst

Smoky quartz

Colors of Varieties of Quartz

Physical Properties of Minerals
3. Streak
 The color of a mineral in powder form

Figure 1.8

Physical Properties of Minerals
4. Luster
 Is the intensity of light reflected from a surface

Pyrite

Potassium feldspar
Galena
Have a metallic luster

Has a nonmetallic luster

Physical Properties of Minerals
5. Cleavage
 Is breakage along planes of weakness
 Is due to weak bonding between those planes

Various Types of Cleavage

Pyramidal, Cubic, and Rhombohedral Cleavage Displayed
by Fluorite, Halite, and Calcite

Fluorite

Halite
Figure 1.11

Calcite

Distinguishing between Cleavage Planes and Crystal Faces

Physical Properties of Minerals
6. Fracture
 Is breakage in random directions
 Is due to the absence of weak bonding between planes
 Conchoidal fracture yields scalloped edges like in broken glass

Physical Properties of Minerals
7. Hardness
 Is the resistance to scratching
 Is based on the Moh’s Scale
 1 talc
 2 gypsum
 3 calcite
 4 fluorite
 5 apatite
 6 potassium feldspar (orthoclase)
 7 quartz
 8 topaz
 9 corundum
 10 diamond

Moh’s
Hardness
Scale

Physical Properties of Minerals
8. Tenacity
 resistance to breaking or bending
9. Specific gravity: an expression of heaviness
density of a substance
SG = ----------------------------------density of water

10. Taste
 Halite (rock salt) tastes salty
11. Magnetism
 magnetite attracts a magnet

X g/cm3
= -------------1 g/cm3

= X

Physical Properties of Minerals
12. Reaction with acid
 minerals containing a CO3 ion fizz (release CO2) when
in contact with hydrochloric acid
2HCl + CaCO3 → Ca2+ + 2Cl- + H2O + CO2
13. Striations
 Are saw-tooth lines present on crystal planes due to
lamellar twinning (repetition) of crystals on that plane
 Striations are characteristic of plagioclase feldspar,
calcite, dolomite, galena, and sphalerite

Elemental Abundances in Continental Crust

Mineral Classes
 Silicate Minerals
 Non-silicate Minerals

Silicate Minerals

 Silicate minerals (silicates) are composed of
silica tetrahedra (SiO4 4-)
 All the common rock-forming minerals are
silicate minerals
 For silica tetrahedra to be stable, they must
either:
 be balanced by positive ions,
 share oxygens with adjacent silica tetrahedra,
or
 substitute one or more Al 3+ for Si 4+

Silicate Minerals

 Compositions of the silicates
 Mafic composition
 Is rich in magnesium, iron, and/or
calcium
 Intermediate composition
 Is compositionally between mafic and
felsic
 Felsic composition
 Is rich in feldspar and/or silica (quartz)

The Silica Tetrahedron
(composed of 4 oxygen atoms surrounding 1 silicon atom)

Two
Illustrations
of the
Si–O4
Tetrahedron

Single Island Silicates
(ex.: olivine)

Single Chain Silicates
(ex.: augite pyroxene)

Single Chain Silicates: The Pyroxenes

Double Chain Silicates: The Amphiboles
(e.g., hornblende)

Sheet Silicates: The Micas
(biotite, muscovite, and the clays)

Framework Silicates:
(potassium feldspar, sodium and calcium plagioclase feldspar, quartz)

The Common Rock-Forming Silicate Minerals

NON-SILICATE MINERAL CLASSES
 Native Elements: consist of only one element.
 Au (gold), Ag (silver), Cu (copper), S (sulfur), C
(graphite, diamond)

 Oxides: contain O 2 Fe2O3 (hematite), Fe3O4 (magnetite), Al2O3 (corundum)

 Carbonates: contain CO3 2 CaCO3 (calcite), CaMg(CO3)2 (dolomite)

NON-SILICATE MINERAL CLASSES
 Sulfides: contain S 2 FeS2 (pyrite), PbS (galena), CuFeS2
(chalcopyrite)

 Sulfates: contain SO4 2 CaSO4.2H2O (gypsum), BaSO4 (barite)

 Halides: contain F 1-, Cl 1-, Br 1-, or I 1 NaCl (halite), KCl (sylvite), CaF2 (fluorite)

Non-silicate Mineral Groups

Native Copper

How do minerals form?
 By crystallization from magma (molten rock material)
 a saturation response

 By crystallization (precipitation) from aqueous fluids
 a saturation response

 By chemical reaction with
 magmatic fluids
 hydrothermal fluids
 water during weathering

 By solid state transformations (metamorphism)
 changes crystal form
 moves ions to new locations
 promotes growth along the edges of mineral grains (crystals) at
the expense of their neighboring mineral grains

Crystallization of Minerals in Cavities:
Geodes

The Effect of Crowding on Crystal Growth

Polymorphs

 Polymorphs are minerals that have the same chemical
composition but a different crystal form
 Graphite and diamond polymorphs of carbon
 Graphite forms at low temperature and pressure
 Diamond forms at high temperature and pressure

 Quartz, stishovite, and coesite are polymorphs of SiO2
 Quartz forms at low to medium temperature and pressure
 stishovite and coesite form at high pressure, such as that
associated with meteor impacts

 Andelusite, kyanite, and sillimanite are polymorphs of
Al2SiO5
 Andelusite is the low temperature low pressure polymorph
 Kyanite is the low temperature high pressure polymorph
 Sillimanite is the high temperature high pressure polymorph

Pseudomorphs
 Pseudomorphs are minerals that have
the same crystal form but a different
chemical composition
 Limonite forms cubic pseudomorphs
after pyrite
 Quartz forms pseudomorphs after
fluorite

MINERAL GROUPS
Non-ferromagnesian
Silicates (K, Na, Ca,
Al)

Ferromagnesian
Silicates (Fe, Mg)

Oxides
Carbonates
Sulfides/sulfates
Native elements