Download Minerals - Geology

Minerals
Standards/Objectives
 Describe
the composition and
structure of Earth’s materials
 Define and describe minerals and
how they form
 Describe the physical properties used
to identify minerals
What is a Mineral?
 Mineral
– is a naturally occurring,
inorganic solid with a definite
chemical composition and crystalline
structure.
 There are about 3800 known
minerals, ~200 are common.
 They are the building blocks of rocks.
States of Matter
Since minerals are solid, what is the
difference between a solid, liquid and gas?
Particle (atom)
Spacing
Particle (atom)
Motion
Volume
Shape
Solid
Very close
Liquid
Somewhat close
Gas
Far apart
Little motion
Vibrate in place
Fixed
Can’t get any
closer
Fixed
No flow
More motion
Able to flow past
Fixed
Can’t get much
closer
Variable, able to
flow to take
shape of
container
Medium
Rapid random
motion
Varies, get
closer or spread
out
Varies
Shape of
container
Relative Energy Lowest
Highest
Animations:
http://chimianet.zefat.ac.il/download/3_states_matter.swf
How do Minerals Form?
 From
the process of crystallization –
the atoms of a gas or liquid come
together to form a solid mineral.
 The atoms are arranged in an
ordered three-dimensional array that
is repeated in all directions.

The crystal grows as more atoms are
added onto the structure.
How do Minerals Form?
 Minerals
can form from a magma as
it begins to cool below its melting
point.
Ex: olivine and feldspar.
Photo: http://skywalker.cochise.edu/wellerr/mineral/olivine/olivineL.htm
Photo: http://www.healthstones.com/mineraldata/mineral
directory/f/feldspar/feldspar.html
How do Minerals Form?
 Minerals
can form as
liquids evaporate
from a solution (like
the crystals you
made in lab). This
process is called
precipitation (the
minerals “fall” out of
the solution like rain
falls out of the sky).
Ex: halite forms from
salt lakes
How do Minerals Form?
Photo: http://www.gccaz.edu/earthsci/
imagearchive/volcanics1.htm
 Minerals
can
also form by
deposition –
when a solid
is formed
from a gas.
Ex: sulfur
forms from
volcanic gas
Photo: http://science.nationalgeographic.com/
science/photos/minerals/
Chemical Composition of Minerals
 Minerals
are made of elements
 Elements cannot be broken into
simpler substances by ordinary
chemical means.
 There are 88 naturally occurring
elements in Earth’s crust.
 There are 92 naturally occurring
elements all together on Earth.
Chemical Composition of Minerals









8 elements make up 98% of the crust:
Oxygen
Silicon
Aluminum
Iron
Calcium
Magnesium
Potassium
Sodium
Chemical Composition of Minerals
 All
minerals are crystalline
solids.
 A crystalline solid is a
substance whose atoms are
arranged in a regular,
orderly, periodically
repeated manner.
 Crystal faces (flat planes)
are the external expression
of the mineral’s internal
atomic structure (i.e., how
the atoms are arranged).
What makes a Mineral Unique?
 There
are two fundamental
properties that distinguish each
mineral from all others: chemical
composition and crystal structure.
What makes a Mineral Unique?
A
mineral’s chemical composition
refers to the elements that form it.
 Ex: Halite (NaCl), or table salt, is
always made of a ratio of 1 sodium
(Na) atom and 1 chlorine (Cl) atom.
 A mineral’s crystal structure refers to
the internal framework of the atoms
that make up the mineral.
Crystal Forms and Systems



The general shape of a crystal (cubic,
octahedral, prismatic…) is called its crystal
habit
If the minerals have enough space, they will
form in their crystalline habit.
Ex: quartz crystals in the shape of points.
If space is limited, they will have a massive
form (can’t see the crystalline habit).
Ex: mass of quartz where can’t see individual
points.
Photo: http://www.crystalminers.com/
Photo: http://www.rocksforkids.com/R&M/quartz.htm
Crystal Forms and Systems


1.
2.
3.
4.
5.
6.
Minerals are grouped into crystal
systems based on their symmetry
(i.e., the angles their faces make to
one another).
There are 6 crystal systems:
Isometric
Tetragonal
Hexagonal
Orthorhombic
Triclinic
Monoclinic
Physical Properties
 Are
used to identify minerals.
 You will be using these properties to
identify minerals in the lab.
Cleavage
 Cleavage
–
tendency of some
minerals to break
along a plane.
 There is a difference
between cleavage
plane (how a
mineral breaks) and
crystal face (how a
mineral grows).
Fracture
Way in which minerals break other
than cleavage (e.g., they do not
break along a plane).
 Types of fracture:
1. Conchoidal – smooth, curved
surfaces

Fracture
2. Splintery - like
ends of split
wood
3. Fibrous – similar
to splintery, but
with a softer
appearance (like
worn cloth)
4. Irregular
Splintery
Fibrous
Hardness
 Resistance
of the surface of a
mineral to scratching.
 It is controlled by the strength of the
chemical bonds.
Hardness

Mohs hardness scale – compares
the relative hardness of minerals.
They are arranged in order of
increasing hardness (1=soft and
10=hard).
Mohs Hardness Scale
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase feldspar
Quartz
Topaz
Corundum
Diamond
2 ½. Fingernail
3 ½. Copper
penny
5 ½. Glass
6 ½. Steel
Specific Gravity
 Weight
of a substance relative to the
weight of an equal volume of water.
 It is a measure of density (mass
divided by volume or D = m/V)
 Ex: a mineral with a specific gravity
of 2 weighs twice as much as the
same volume of water.
Color
 Most
obvious property of minerals.
 Not a reliable way to identify
minerals. Remember the same
mineral can come in many different
colors.
The many colors of quartz
Streak
 Color
of the fine powder of a mineral.
 More reliable for identification than
color.
Luster
How a mineral reflects light.
 Two main categories:
1. Metallic – looks like metal surface.

Luster
2. Nonmetallic – if nonmetallic, must
be classified as:
a. vitreous – glassy
b. pearly – whitish, pearl-like
iridescence
c. earthy or dull
Luster
d. resinous - like amber
or rosin
e. greasy – looks like
it’s covered by a thin
layer of oil (rainbow of
colors)
Tenacity

1.
2.
3.
4.
5.
6.
Resistance of a mineral to breakage.
Brittle – breaks and powders easily.
Malleable – can be hammered into
thin sheets.
Sectile – can be cut into thin
shavings with a knife.
Ductile – can be drawn into a wire.
Flexible – bends but does not resume
original shape (ex: copper).
Elastic – bends and regains original
shape (mica).
Acid Reactivity
 Effervesces
(bubbles) when drop of
hydrochloric acid (HCl) is placed on
it.
Magnetic
 Is
attracted to a magnet or picks up
iron filings.
Fluorescence
 Emits
visible light when exposed to
ultraviolet (UV) radiation.
Phosphorescence
 Continues
to emit light after external
light source is taken away.
Mineral Classifications
 Silicates
– minerals containing silicon
(Si) and oxygen (O). Most abundant in
Earth’s crust. Make up 95% of crust.
 Carbonates – contain carbon (C) and
oxygen (O).
 Oxides – composed of oxygen and
metals.
 Sulfides – contain sulfur (S) and metals.
 Sulfates – made up of sulfate (SO4-) and
metals.
Rock Forming Minerals
Silicates – are the most
common minerals that make
up rocks.
1. Feldspar – most abundant
mineral, 50% of Earth’s crust.
a. orthoclase feldspar – contains
potassium (K).
b. plagioclase feldspar –
contains calcium (Ca) and
sodium (Na).
2. Quartz – 2nd most abundant
mineral, SiO2.

Rock Forming Minerals
3. Pyroxene – Ex: augite
4. Amphibole – Ex: hornblende
5. Mica – Ex: muscovite
6. Clay minerals – ex: kaolinite
7. Olivine