Minerals





WHY?
Why do we learn about rocks and minerals?
What is their importance?
What are they used for?
How do we identify them?
How can we be sure they are what we think
they are?


Garnet is a gemstone composed of metals (calcium, magnesium, iron, aluminum, and/or
chromium) bonded to silica. It has a relatively high hardness, harder than silica sand, so small
grains are used as an abrasive for both sand blasting and in sand paper.
In contrast, talc, used in baby powder, is a very soft mineral. It is composed of magnesium and
silica, bonded with water, so it has some of the same elements as garnet, but the arrangement
of its mineral structure makes it very weak -- hence its softness. Soapstone is composed
primarily of talc.


The rocks on this shelf are
produced by volcanic
eruptions. Obsidian forms
when lava cools very
quickly, forming natural
glass. It can be broken to
produce extremely hard,
sharp edges, which many
cultures have used for
projectiles and knives.
Even today, some surgical
scalpels are made from
obsidian, as seen at the
lower right of the image.
Pumice is also formed by
rapid cooling of lava. In
this case, the lava is
cooling as dissolved
gasses are escaping,
creating a large number
of frozen bubbles in its
structure. Imagine
freezing a shaken-up cola
as it foams out of the
bottle. Pumice is used as
an abrasive, illustrated
here by pre-faded jeans,
weathered by rubbing
with pumice, and Lava
brand soap, which
includes pumice as a
scouring agent for
cleaning extra-dirty
hands.


Copper is used in the
manufacture of electrical wire,
copper pipes for water, copper
cookware, and in the computer
you're using to view this web
gallery. Copper has low
resistence to electrical charge
and is relatively abundant,
compared to its elemental
sisters, gold and silver, which is
why it's used for wiring. It can
be found both in its elemental
state and as an ore, in which the
copper is bonded to other
elements.
Zinc has been reported as
beneficial in shortening the
duration of common colds, so it
is often included in over the
counter cold remedies. There
have been no conclusive results
supporting this use, but zinc is
an essential element, so taking it
as a supplement in reasonable
doses cannot have any adverse
effects. Zinc is often found
naturally in sphalerite, a mineral
including sulfur and iron. Zinc is
also used for galvanizing,
because it is relatively inert
compared to steel, so it can
prevent rusting when used as a


It's hard not to experience iron and
aluminum in our everyday lives.
Iron ores are usually compounds of
iron and oxygen, otherwise known
as rust. Much of these ores were
formed when the earliest
photosynthesizing microbes began
to pump oxygen into the earth's
oceans. In a way, iron ores are
fossils, so all iron and steel we use
are made from fossils. Iron is
commonly used in different
compound with carbon and silicon.
Different ratios of the other
elements determine its physical
properties, which vary between cast
iron, as in the frying pan, and steel,
as in the reusable coffee cup.
Aluminum is found naturally as
bauxite, made of aluminum bonded
with water. Purifying bauxite used to
be expensive and slow, so
aluminum was a rare and valuable
metal in the 18th and 19th
centuries. That's why the top of the
Washington monument was covered
in aluminum -- it was like covering
it in silver! Since the late 1880s,
aluminum ore has been purified
using electricity, and it has become
cheap and plentiful. Benjamin
Franklin would think we all live like
kings if he knew that we casually
drink out of aluminum cans and use
aluminum foil to save our leftovers.

This shelf features silver and gold, sister elements to copper. On the periodic table they're all in the same
column, and that reflects the similar structures of their atoms, which give them similar chemical properties.
They're all good conductors of both heat and electricity. Gold and silver are actually better conductors than
copper, which is why they're used in high-end electronic devices, like cell phones and some audio equipment.
They're rarer than copper, too, which is why gold and silver jewelry is more valuable and why they're used
more often for decoration than for their electrical properties. Gold is most often found as a pure element in
nature, but silver is often found both in its pure form and in ores.


This shelf features mercury and lead, two important dense metals. Mercury is the only metal that is liquid at
room temperature, which is why it has been used for so long in thermometers. As the metal expands and
contracts in response to the temperature, it moves up and down the thin tube, and allowing the temperature to
be read. Elemental mercury is poisonous, producing mental and coordination problems, so people have moved
away from mercury thermometers and other everyday uses. Mercury is not found as a pure element in nature.
It is mined from mercury ores, such as cinnabar (also called vermilion). Cinnabar is composed of mercury and
sulfur and has been used as a red pigment since ancient times.
Lead is a very dense, very soft metal and has a low melting point, which allows it to be easily formed. Its
density and easy of forming have made it the most common metal for bullets since the origin of firearms. It
has also been used for fishing weights, as illustrated here. Its density is so great that it is used as a radiation
shield. We most often see it in dentists' offices in the lead apron we wear to protect us from X-rays, but it is
also used to shield nuclear reactors because it can capture any stray radiation before it enters the
environment. Lead is, like mercury, poisonous, so it is beginning to fall out of everyday use. Its most common
use today is in the lead-acid batteries found in automobiles. Lead is found in nature most often as galena, a
compound with sulfur.

The concrete that makes up most of the urban landscape is actually an artifical reconstruction
of a naturally occurring rock, conglomerate. To make concrete, we mix sand and gravel, with
cement. Cement is created by heating ground limestone with other minerals. When hot
enough, the limestone releases carbon dioxide and becomes quicklime, the primary ingredient
in cement. When the quicklime in cement reacts with water, it forms a stable crystal: this is
what happens when concrete 'dries'. The process of making cement from limestone releases
carbon dioxide, consequently, the cement industry is second only to power production in the
release of carbon dioxide gas into the atmosphere.

When we describe oil and coal as fossil fuels, we mean it: they are produced by the
cooking of decomposed plant and animal matter deep in the earth's crust over
many millions of years. Fossil fuels are a form of solar power: they are energy from
the sun trapped by plants millions of years ago. Oil is formed in oil shales, but once
it becomes liquid it tends to rise until it is trapped in a porous reservoir rock, like
the ones shown here. Drilling into the reservoirs releases the oil for human use.
Finding oil is a tricky proposition, combining the science of geology with the art of
imagining where the oil would flow within the crust.



When we describe oil and coal as fossil fuels, we mean it: they are produced by the cooking of decomposed plant and
animal matter deep in the earth's crust over many millions of years. Fossil fuels are a form of solar power: they are
energy from the sun trapped by plants millions of years ago. Coal is simply the remains of woody plants that died in
swampy conditions and was cooked down into a solid mass. Large amounts of wood accumulated on earth during the
Carboniferous period, 359 to 299 million years ago, because plants evolved wood and no organisms on earth evolved the
ability to digest wood for 50 to 60 million years! Think of a world where tree trunks never decompose because there are
no microbes that know how to break them down. That's the Carboniferous world that left us with a legacy of coal.
Graphite is elemental carbon, just like diamond. The difference is that diamond forms at extremely high pressures, which
cause the carbon atoms to line up in a strong mineral. Graphite is formed under much lower pressures and has a mineral
structure that makes it slippery and easy to break. We use it for the 'lead' in pencils because it makes a good, but
erasable, mark. We also use it as a powder for lubrication.
Both coal and graphite are composed primarily of carbon.


Here we see some of
the many products
made from petroleum,
or crude oil. Oil is used
as a machine lubricant,
as with the 10W-40 oil.
All of the rubber and
plastics here are made
from oil, including the
gas can. The gas can
also represents
gasoline, the
ubiquitous fuel that is
refined from crude oil.
Diesel fuel is also
refined from crude oil.
Some scientists have
suggested that future
generations will be
amazed that we burned
so much of our oil as
fuel, instead of using it
for more permanent
applications like
plastics.
Try to think of a day in
your life without
plastic.
Minerals must
occur naturally.
 Cannot be humanmade.
 Cement, bricks,
steel, and glass all
come from
materials found in
the earth, but
these are made by
people.

Naturally Occurring
Inorganic
materials were
never living.
 Coal is made
from the
remains of
ancient plants
and animals, so
coal is not a
mineral.

Inorganic
What defines
a “mineral”





Naturally occurring
Inorganic
Solid
Crystal structure
Definite chemical
composition
Minerals
The state of matter
when the material
is below its
freezing point.
 Definite shape,
definite volume.
 Particles are fixed
in place.

Solid
Is Water a Mineral?
The particles of the
material line up in
a regular, repeating
pattern.
 Has flat sides
called faces, that
meet at sharp
edges and corners.

Crystal Structure



Always contains
certain elements in
the same proportion.
Almost all minerals are
compounds, which are
two or more different
elements bonded
together.
Pyrite is two sulfur
atoms bonded with an
atom of iron.
Definite Chemical Composition
2H means two
Chemical Formulas separate hydrogen
atoms.
 Have a definite
 H2 mean two
format.
bonded hydrogen
 Written together
atoms.
means they are
bonded.
 H2O means two
 Coefficients tell how
hydrogen atoms
many of the whole
bonded with an
thing you have.
oxygen atom.


Subscripts tell how
many of the atom
before it that you
have.
2 H2O means you
have two separate
water molecules,
each containing
two hydrogen and
one oxygen atom.
 Bornite is a copper
ore that turns
purple when
exposed to air. It’s
formula is Cu5FeS4.

More Formulas
So how many of
each atom are
present?
 Five copper
 one iron
 four sulfur

Identifying Minerals







Each mineral has
specific properties
that can be used to
identify it.
Habit
Hardness
Luster
Color
Streak
Opacity (transparent,
translucent, opaque)


Cleavage and Fracture
Special Properties

Habit refers to the overall shape of the
mineral. Scientists use terms like: "equant" (3
dimensions of the mineral have about the
same length, like a cube or sphere),
“elongate" (one direction is long but the other
2 are short, like a pencil), or "platy" (one
dimension is short, other 2 are long like a
sheet of paper)
Crystal Habit
A measure of how
easily a mineral
can be scratched.
 Determined by the
atomic structure of
the mineral.
 Friedrich Mohs
developed the
scale we use today.
 Try to commit to
memory.

Hardness
The way a mineral
reflects light.
 Can be metallic or
non-metallic.
 Shiny or dull.
 Earthy, waxy,
pearly, glassy,
resinous.

Luster
Surface color of
the mineral.
 Not especially
useful in
identifying
minerals, as some
minerals like
quartz can come in
a variety of colors.

Color
Minerals will have a
certain density
regardless of the
size of the sample.
 When geologists
compare the weight
of the mineral to the
weight of an equal
volume of water it is
called specific
gravity.

Density (Heft)
The color of its
powder.
 Not always the
same as the color
of the mineral.
 Pyrite has a gold
color, but its streak
is a greenish black.
 Streak test.

Streak
Tenacity
Cleavage Refers to very
smooth, flat, shiny breakage
surfaces
These special breakage
surfaces correspond to
zones of weak bonding in
the crystal structure.
To describe cleavage, one
must determine the number
of unique cleavage planes
(directions) and their angle
with respect to each other
(e.g. salt breaks into cubes,
with cleavage in 3
directions, all at 90
degrees)
Cleavage
NO CLEAVAGE
 Refers
to
how light
passes
through the
mineral (if
at all).
Opacity
(transparent, translucent, opaque)
Some minerals are
magnetic (i.e.,
magnetite)
Some minerals
effervesce ("fizz")
in dilute acid
(calcite)
Specific gravity (like
density) galena has
a high specific
gravity.


Calcite has “double
refraction”
Fluorite glows in a UV
light
Special Properties
Things to do…
Create mineral identification chart (10
columns, 30 rows).
 Retrieve a laptop computer for each team.
 Listen to MINERAL RULES.
 Organize minerals; practice identification

◦ http://www.minsocam.org/msa/coll
ectors_corner/id/mineral_id_keyq1.
htm
http://www.minso
cam.org/msa/coll
ectors_corner/id/
mineral_id_keyi1.
htm
www.quia.com/pages/jwhite/minerals
http://www.minsocam.org/msa/collect
ors_corner/id/mineral_id_keyq1.htm
BARITE
Barite
BAUXITE
Bauxite
BIOTITE
Biotite
CALCITE
Calcite
CHALCOPYRITE
Chalcopyrite
FLUORITE
Fluorite
GALENA
Galena
GARNET
Garnet
GRAPHITE
Graphite (in Schist)
HALITE
Halite
HORNBLENDE
Hornblende
LABRADORITE
Labradorite
LIMONITE
Limonite
MAGNETITE
Magnetite
MASSIVE GYPSUM
Rock Gypsum (massive)
MASSIVE HEMATITE
Massive Hematite
MICROCLINE
Microcline (Orthoclase)
MUSCOVITE
Muscovite
OLIVINE
Olivine
OOLITIC HEMATITE
Oolitic Hematite
PYRITE
Pyrite
ROSE QUARTZ
Rose Quartz
SELENITE
Selenite (gypsum crystal)
SERPENTINE
Serpentine
Specular Hematite
SPECULAR HEMATITE
SPHALERITE
Sphalerite
SULFUR
Sulfur
TALC
Talc
QUARTZ CRYSTAL
Quartz Crystal