Download I. What is a Mineral?

Chapter 13
Minerals
of
The Earth’s Crust
I. What is a Mineral?
-a naturally formed, inorganic
solid that has a definite
crystalline structure.
Mineral Structure
To be a mineral, a
substance must
• be a solid
• be inorganic
• have a
repeating inner
“crystalline”
structure
• be formed in
nature
Atoms & Compounds
Minerals are made up of atoms
of one or more elements.
Elements are pure substances
made of only one kind of
atom. They cannot be broken
down into simpler substances
by ordinary means.
An atom is the smallest
part of an element that
has all the properties of
that element.
Atoms & Compounds cont.
Compounds are substances
made of 2 or more elements
that have been chemically
combined. Example: NaCl
(salt) is a compound made of
Na (sodium), a metal, and
Cl (chlorine), a gas. Most
minerals are made of
compounds but some
are composed of just
one element and are
called native elements.
Crystals
Solid, geometric forms of minerals produced by a
repeating pattern of atoms or molecules that is
present throughout the mineral are called
crystals. Each crystal
has a definite shape
determined by the
arrangement of atoms
or molecules within the
crystal, and each mineral has
a definite crystalline structure. Minerals can be
grouped into classes according to the crystals they
form.
Silicate Minerals
Minerals are divided into 2 groups based on
their chemical composition:
Silicate minerals-minerals that contain a
combination of silicon and oxygen, Earth’s 2
most common elements that make up more
than 90% of the Earth’s crust.
Examples: quartz, feldspar, and mica
quartz
feldspar
mica
Nonsilicate Minerals
are minerals that do not contain a
combination of the elements silicon and
oxygen.
Some are made up of elements such as
carbon, oxygen, fluorine and sulfur.
Examples:
copper, calcite, fluorite, corundum,
gypsum, galena and others.
galena
copper
calcite
fluorite
corundum
gypsum
II. Mineral Identification
Color
The same mineral can
come in a variety of
colors, depending on
what impurities are
present and exposure
to air and water for
long periods of time.
Color is not the best way
to identify a mineral.
-is the way a
surface
reflects light
-Example: is
something
shiny or dull
metallic-bright,
reflective
submetallic-dull,
metallic or
nonmetallic
nonmetallic6 different
descriptions
Luster
Streak
-Streak is the color of a mineral
in powdered form
It can be found by rubbing the
mineral against a piece of
unglazed porcelain called a
“streak plate”
The color of a mineral’s streak is
not always the color of the
mineral sample, and is not
affected by air or water. Streak is
more reliable for identification
than color.
Cleavage and Fracture
The way a mineral breaks is
determined by the
arrangement of its atoms.
Cleavage is the tendency of
some minerals to break
along smooth flat
surfaces.
Fracture is the tendency of
some minerals to break
unevenly along curved or
irregular surfaces.
Hardness
This is a mineral’s resistance to being scratched.
Scientists use the
Mohs Hardness Scale shown below. Talc has a rating of
1 and diamond has a rating of 10. If the reference
mineral scratches your mineral, then the reference
mineral is harder than your mineral.
MOHS HARDNESS SCALE
Density
This is the measure of the amount of matter in a given amount of
space. It is a ratio of an object’s mass to it’s volume. Water
has a density of 1 g/cm³ and so is used as a reference point for
other substances. The ratio of an object’s density to the
density of water is called its specific gravity.
Gold has a specific gravity of 19 and so contains 19 times as much
matter as 1 cm³of water contains. Pyrite (fool’s gold) has a
specific gravity of 5. Specific gravity can be used to
distinguish between gold and “fool’s gold”.
specific gravity ~ how heavy something feels when compared to
what you would expect, heft, weight, mass, density
Gold on chunk of
pyrite-”fool’s gold”
Special Properties
The following special properties help identify a few
types of minerals:
Fluorescence-calcite and fluorite glow under
UV light
Magnetism-magnetite and pyrrhotite are
natural magnets that attract iron
Chemical reaction-calcite will become bubbly
or “fizz” when a drop of weak acid is
place on it
Taste-Halite has a salty taste
Optical Properties-Calcite will cause a
double image when placed over an image.
Radioactivity-Minerals that contain radium
or uranium can be detected by a geiger
counter
III. The Formation, Mining and
Use of Minerals
Minerals
form in a
variety of
environments
in the Earth’s
crust with
different
physical and
chemical
conditions
which
determine
the mineral
properties.
Surface Mining
When mineral deposits are located at or near
the surface of the Earth, surface-mining
methods are used to remove the minerals.
Mineral deposits called ores are mined
for profit through surface or
subsurface mining.
The method miners choose depends
on how close to the surface or how far
down in the Earth the mineral is
located.
Open-Pit Mining
•is used to remove
large, near-surface
deposits of
economically important
minerals such as gold
and copper.
•is mined downward,
layer by layer
•explosives are used to
break up the ore
•ore is loaded into
trucks and taken away
for processing
Open-Pit Mining
Trucks the size of houses dump 200-ton
loads of waste rock, remnants of mineral
mining from an open pit mine in Nevada.
Quarries
Are open pits used to mine building
stone, crushed rock, sand and gravel
Strip Mining
Surface mining of coal is done in strips that may
be 50m wide and 1 km long
Subsurface Mining cont.
Subsurface Mining
This method
is used when
mineral
deposits are
too deep
within the
Earth to be
surface
mined.
Subsurface Mining continued
Subsurface mining often requires that passageways be
dug into the Earth to reach ore. These passageways
may be dug horizontally or at an angle.
Subsurface Mining continued…
Sinkholes can
result!
Wall of coal-mining pit near
Haybro, Colorado
Responsible Mining
Mining can destroy or disturb the habitats of plants and
animals. The waste products from a a mine may get into
water sources, which pollutes surface water and
groundwater.
Mine Reclamation
When land used for mining
is returned to its original
state or better, it is
called reclamation.
During Mining
After Reclamation
The Use of Minerals
1 Common Uses of Minerals
Mineral
Uses
Copper
electrical wire, plumbing, coins
Diamond
jewelry, cutting tools, drill bits
Galena
batteries, ammunition
Gibbsite
cans, foil, appliances, utensils
Gold
jewelry, computers, spacecraft, dentistry
Gypsum
wallboards, plaster, cement
Halite
nutrition, highway de-icer, water softener
Quartz
glass, computer chips
Silver
photography, electronics products, jewelry
Sphalerite
jet aircraft, spacecraft, paints
Uses of Minerals
Metallic Minerals
have shiny surfaces
good conductors of heat and electricity
can be processed into metals that are
strong and do not rust
other metals can be pounded or pressed
into various shapes
metallic minerals that have many
industrial uses are gold, silver, and
copper.