MINERALS
GeoFacts
•Stalactites and other cave formations made from
calcium carbonate take thousands of years to form.
•One estimate is that a stalactite will grow only 10
cm every 1000 years.
What is a mineral?
 Five characteristics of all minerals:
 naturally occurring
 inorganic (was never alive)
 definite crystal structure (atoms arranged in an
orderly pattern)
 solid
 specific chemical composition (made up of different
elements and compounds)
 Earth’s crust is composed of about 3000
minerals.
Naturally occurring and inorganic…
 Minerals are formed from natural processes
 Any man-made mineral is called synthetic
 Minerals are inorganic because they are not alive
and never were alive
 Salt is a mineral, but sugar is not. Sugar comes
from plants.
 Coal is not a mineral because it forms over
thousands of years from the buildup of
dead/decaying matter.
Definite crystal structure
 The atoms in minerals are arranged in regular
geometric patterns that are repeated.
 This regular formation is called a crystal
Solids with specific compositions
 Solids have definite shapes and volumes; liquids
and gases do not.
 Many atoms have silicon and oxygen in them,
but the arrangement and proportion of elements
in these minerals are unique.
 The formula for quartz is SiO2
 The formula for pyroxene is MgSiO3
Common elements found in minerals
 Eight elements make up 98.5% of the crust’s
total mass:
Name
Symbol
% by Mass
Oxygen
O
46.6
Silicon
Si
27.7
Aluminum
Al
8.1
Iron
Fe
5.0
Calcium
Ca
3.6
Sodium
Na
2.8
Potassium
K
2.6
Magnesium
Mg
2.1
 More than 90% of the minerals in Earth’s crust
are compounds containing OXYGEN AND
SILICON, the two most abundant elements.
 Most minerals are compounds.
 Quartz is a compound of silicon and oxygen
 Galena is a compound of lead and sulfur
 A few minerals consist of single elements and
are called native elements:
 Examples: silver, copper, sulfur and diamond
Rock-forming minerals
 There are 8 minerals that make up most of the
rocks of Earth’s crust.
 They are primarily composed of the eight most
common elements in Earth’s crust.
 Quartz, feldspar, mica, pyroxene
 Amphibole, olivine, garnet, calcite
 We’ll talk more about rocks next chapter
Structure of minerals
Identifying minerals
 Mineralogy – the study of minerals and their
unique properties
 Minerals are RARELY identified by one single
property
Mineral properties
Color – not the most reliable characteristic; minerals
change color with a change in temperature,
pressure or metal
Mineral properties
Luster – describes how minerals shine in natural light


We classify minerals as having metallic or non-metallic
luster. Not all metallic minerals are metals!!
We further classify using words such as vitreous, pearly,
greasy, oily, dull, earthy
Mineral properties
Streak – the color of a mineral’s powder; in many cases
the streak will not be the same color as the mineral.
 The streaks of nonmetallic minerals are usually colorless
or white
Mineral properties
Hardness – resistance to being scratched
 Diamond is the hardest of all minerals.
 Talc is the softest of all minerals.
The minerals in the table on the next slide were
selected because they are easily recognized and are
readily found in nature (except for diamond).
Mohs Scale of Hardness
 Friedrich Mohs
devised a numeric
scale that is used to
express the
hardness of
minerals.
 You can determine
the approximate
hardness of any
common mineral by
using other common
objects
Mineral
Hardness
Comparison
Talc
1
Gypsum
2
Fingernail = 2.5
Calcite
3
Copper penny = 3.5
Fluorite
4
Iron nail = 4.5
Apatite
5
Glass = 5.5
Feldspar
6
Steel file = 6.5
Quartz
7
Streak plate = 7
Topaz
8
Corundum
9
Diamond
10
Mineral properties
Specific gravity – ratio of
a mineral’s mass to the
mass of an equal
volume of water
It tells you how many
more times denser the
mineral is than water.
Mineral properties
Texture – the way a mineral feels
This property is very subjective; a mineral may feel
different to two people working together
Special properties
 HCl chemical test: look for bubbles to form
 Double refraction: shows a double image
 Fluorescence: the ability to glow under UV light
 Phosphorescence: the ability to glow in the dark
 Magnetism: attraction to magnets
Silica Tetrahedron
 More than 90% of the
minerals in Earth’s
crust are silicates.
 Silicon and oxygen
bond in a way that
forms a tetrahedron
Mineral groups
 Silicates – quartz and feldspar are the most
common minerals found in this group
 Uses: gems, watches, potting soil additive
 Carbonates – calcite and dolomite are the most
common minerals
 Uses: cement for construction, paper, medicines
Mineral groups
 Oxide – mineral that has oxygen combined with
a metal element; hematite and magnetite are
common minerals
 Uses: abrasives, plumbing fixtures, auto parts
 Sulfide – mineral that has sulfur combined with a
metal element; pyrite (fool’s gold) and galena are
common minerals
 Uses: jewelry, ores for manufacturing
Mining for minerals
Ores and mines
 Ore – minerals that contain useful substances
that can be mined for a profit
 The classification of a mineral as an ore can also
change if the supply of or demand for that
mineral changes.
 Ores that are located deep within Earth’s crust
are removed by mining
 Consequence of mining???
Gems
 Some minerals are rarer than others and are
therefore classified as expensive gems.
 Gems – valuable minerals that are prized for
their rarity and beauty
 Rubies and emeralds are more expensive than
diamonds.