MINERALS

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MINERALS
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What is a mineral ?

• Naturally occurring
• Inorganic
• Solid
• Crystal shape
• Definite chemical composition

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Naturally occurring
Meansthey are not made by humans (they are
formed by the earth).
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Inorganic
Means.. they have never been alive and are
not made of plants or animals.
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Solid
Means.they are solids, not liquids (like
water), or gases (like the air around you)
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Crystal shape
Meansthey have an ordered atomic arrangement.
The chemical elements that make up each mineral
are arranged in a particular way - this is why
minerals grow as crystals.
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Definite chemical composition
Sulfur (S) - element
Halite (NaCl) - compound
Means..each mineral is a pure substance.
Minerals can be elements or compounds.
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QUIZ
Charcoal
Hematite
Not
Mineral
As we go through the next few slides, decide (in
your head) whether each substance is a mineral or
not.
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Mineral or Not ?
Quartz
Think about it. Does anybody make quartz? Where
do you think it is found? Does it have a crystal
structure?
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Mineral
Quartz is a mineral. You have probably seen a
quartz crystal in a museum or rock shop. It is a
naturally occurring, inorganic, solid, with a
definite chemical composition, and an ordered
atomic arrangement!!!
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Mineral or Not ?
Plastic
Think about it. Who makes plastic? It may look
pretty inorganic, but do you know what plastic is
made from?

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Not
Plastic is not a mineral. Plastic is not
mineral. It is a solid, and it has a definite
chemical composition. However its atoms do not
have a crystal shape. Plastic is made from oil
(an organic material) by humans - plastic is not
a naturally occurring substance. Plastic is not a
mineral.

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Mineral or Not ?

Gold
Think about it. Can you make gold? You can
make gold jewelry, but where do you find gold
nuggets? Does it have a crystal shape?

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Mineral
Gold is a mineral. You may think of it as a
metal, but native gold is a mineral too. It is a
naturally occurring, inorganic, solid, with a
definite chemical composition, and an ordered
atomic arrangement (crystal shape) !!!


Gold crystal ?
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Mineral or Not ?


Granite
Think about it. What do you think it is made
of? It has lots of different types of crystals,
and they are all jumbled up together. Does it
occur naturally?

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Not

Granite is not a mineral. Granite is a rock and
not a mineral, but rocks are made of minerals.
The minerals in granite - quartz, mica and
feldspars - are all jumbled together. Some
granites have more quartz than others granite
does not have a fixed chemical composition.
Remember, rocks are made up of minerals, but that
doesn't mean that rocks ARE minerals.


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Tests for Identifying Minerals
It is very difficult to tell one mineral from
another just by looking at it. We will use
several tests and resources in order to identify
a mineral.
Are the two minerals on this page the same
mineral or different minerals?
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DIFFERENT
Cinnabar
Beryl
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Try this one.
Are these the same mineral or different minerals?
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S A M E
Gypsum
Gypsum
Gypsum
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Tests for Identifying Minerals

1. Color
2. Luster
3. Streak
4. Hardness
5. Density
6. Crystal shape
7. Cleavage and/or Fracture (Breakage)
8. Special Properties

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1. Color
Most minerals have a variety of colors. All of
the samples above are quartz.
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Color can also be unreliable because it can
change.
Chalcopyrite (gold color) with quartz (colorless)
Chalcopyrite after being exposed to the weather.
Some minerals have metals in them which can
oxidize or rust when exposed to the weather.
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Silver
Gold is one of the only metals that will not
oxidize (rust or tarnish) when exposed to the
elements - which is why it is a good choice for
jewelry.
Tarnished silver
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Be very specific when recording colors !
green silvery -yellow gray grayish-black silver
black golden gold-colored yellow bronze brown
copper-colored silvery-white with black specks
white colorless beige dirty-white red purple m
auve pink salmon pink blue bluish turquoise

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How would you describe the color of these
minerals ?
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2. LUSTER
Luster describes the way a mineral reflects light.

• There are two types of luster
• Metallic
• 2. Nonmetallic

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Metallic Luster
Copper
Magnetite
Silver
Magnetite
Gold
Galena
Hematite
Pyrite
Metallic luster is shiny like a metal. (dont
forget that minerals with metals in them can
tarnish or rust)
Graphite
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Nonmetallic Luster
Malachite (waxy)
Beryl (aquamarine) (glassy or vitreous)
Kaolinite (earthy)
Diamond ?(greasy) (brilliant)?
Muscovite mica (pearly)
Luster that does not look like a metal. With
nonmetallic luster, you need to specify the type.
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Words that describe non-metallic lusters
Luster Description dull / earthy very dull
looks like earth waxy looks like a chunk of
wax   greasy / oily has a oily, reflective
surface   pearly like a pearl, play of
colors, light silky / velvety looks like it
has a soft, smooth surface   resinous looks
like dried glue or gum, usually
yellow-brown glassy / vitreous looks like
glass adamantine high luster, almost
brilliant brilliant looks like a gem
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Check yourself. What type of luster is shown ?
Metallic or Nonmetallic ?????
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Biotite mica (nonmetallic - pearly)
Chalcopyrite (metallic) Quartz (nonmetallic -
glassy or vitreous)
Goethite (nonmetallic -earthy)
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3. Streak
Streak is the color of the powder left by a
mineral when it is rubbed against a hard, rough
surface (streak plate) .

• Good test, except when
• Mineral is harder than 7 (mineral is harder
  than streak plate)
• Mineral is a light color (when using a white
  streak plate)

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What color would you expect the streak to be for
these two elements ?
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Earthy hematite
Metallic hematite
Both of these minerals are hematite, so they will
produce, basically, the same color streak.
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4. Hardness
Hardness is the ability of a mineral to resist
being scratched.
Very useful test, but often incorrectly performed

• Two Hardness Scales
• Mohs Hardness Scale
• Field Hardness Scale

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• Mohs Hardness Scale
• Scale goes from 1 - 10
• Different minerals represent different
  hardnesses

• Field Hardness Scale
• Scale goes from 1 - 7
• Different instruments are used to measure
  hardness

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Mohs Hardness Scale

• ? Scale goes from 1 - 10
• Different minerals represent different
  hardnesses

6 - Feldspar 7 - Quartz 8 - Topaz 9 -
Corundum 10- Diamond
1 - Talc 2 - Gypsum 3 - Calcite 4 -
Fluorite 5 - Apatite
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Field Hardness Scale
Hardness Common Test 1
Easily scratched with fingernail (2.2) 2
Scratched by fingernail (2.2) 3
Scratched by a copper penny
(3.5) 4 Scratched easily by a
pocket knife (5.2) (or a common nail), but
will not scratch glass 5
Difficult to scratch with a knife (5.2) (or
a common nail) barely scratches glass
(5.5) 6 Easily scratches glass
(5.5) 7 Easily scratches glass (5.5)
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Helpful hints for conducting the hardness test

• Each mineral can scratch the minerals with
  lower hardness ratings.
• Each mineral can scratch itself.
• Dont press hard, normal scratching should
  do.
• Weathered surfaces are softer.
• Corners or edges of crystals are softer.
• Small pieces seem softer than large pieces.
• When you scratch, take a close look at the
  scratch line- which often looks white.
• Is it really a scratch, or is it a
  powder line made from the tool you used
• because it was softer than the item you
  were trying to scratch.

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5. Specific Gravity (Density)
This characteristic relates to the minerals
density. If the mineral is heavy for its size,
then it has a high specific gravity. Water
displacement is useful in determining specific
gravity.
Specific gravity is only helpful if the sample is
pure.

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6. Crystal Shape
Crystal shape is the repeating atomic pattern
within the mineral. Each mineral has a certain
crystal pattern when the mineral is forming.

• There are 6 crystal forms
• Cubic
• Hexagonal
• Orthorhombic
• Monoclinic
• Tetragonal
• Triclinic

You will seldomly see minerals in their crystal
form in class.
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Cubic
Cubic crystals are not always cube shaped! There
are many that are shaped like octahedrons (eight
faces), and some that are shaped like
dodecahedrons (10 faces).
Orthorhombic
Orthorhombic crystals are often shaped like
rhombic prisms or dipyramids (two pyramids
stuck together). They often look a bit like
tetragonal crystals except that they are not
square in cross section (when you look at the
crystal on end).
Tetragonal
Tetragonal crystals are shaped like cubic
crystals but are longer in one direction making
shapes like double pyramids and prisms.
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Hexagonal
Hexagonal crystals often look like six-sided
prisms. When you look at the crystal on end, it
looks like a hexagon shape in cross section.
Monoclinic
Monoclinic crystals look like tetragonal
crystals that have been skewed. They often
form prism shapes and double pyramids.

Triclinic
Triclinic crystals are sometimes very strange
shapes! They are usually not symmetrical from
one side to the other.
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7. Breakage (Cleavage and Fracture)
Cleavage is when a mineral breaks on a smooth,
definite surface.
You will not actually break the minerals but look
at how they have broken in the past.
Fracture is when a mineral breaks unevenly or
with a rough break.
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Cleavage
Words associated with Cleavage perfect fibrous
90 ? books plates octahedral dodecahedral cubi
c basal hexagonal prismatic (prism) two
planes monoclinic sheets rhombohedral ___
directions (ex. 2 directions, 4 directions)
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Fracture
Words associated with fracture Conchodial Uneven
Imperfect Irregular Fracture Hackly No cleavage
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8. Special Properties
Some minerals have special properties.
For example Magnetism Fluorescent Unusual taste
or smell Effervesces (fizzes) in acids
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Magnetism
MAGNETISM Some minerals containing iron can be
magnetic. They act just like the refrigerator
magnets you find at home. Magnetite (iron oxide)
is the only common mineral that is strongly
magnetic. The simplest test for magnetism is to
use a compass. A magnetic material will move the
needle away from its usual position, pointing
northwards. In the picture on the right,
paperclips are attracted to the mineral magnetite.
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Taste This will quickly identify the mineral
halite (salt). If you are new to this process you
must use this one with caution, as you never know
what the unknown may be. If you were to taste
the sample (especially in a class environment),
you should realize that it has been handled by
and probably tasted by hundreds of others. YUCK
!!!
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Reaction to Acid
The carbonate minerals react with dilute
hydrochloric acid (HCl) by fizzing, producing
bubbles of carbon dioxide gas (the same type of
harmless gas bubbles that are found in carbonated
beverages). Calcite fizzes readily in
hydrochloric acid. Dolomite will fizz if it is
first scratched and powdered. You may use a nail
or steel needle probe to scratch the specimen to
try this test.
CaCO3 2HCl gt CaCl2 H2O CO2
(calcite) (hydrochloric acid)
(calcium chloride) (water) (carbon
dioxide)
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Birefringence
Birefringence
Optical Calcite
This is also known as double refraction.
Birefringent minerals split the light into two
different rays which gives the illusion of double
vision as in this calcite.
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Fluorescence
Some minerals display what is called the
phenomenon of photoluminescence. This basically
means that they "glow" when exposed to UV light
(black light). The mineral fluorite is often
strongly fluorescent.
Benitoite
Willemite
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Special Properties of Ulexite
This specimen of Ulexite that has been cut top
and bottom with a diamond saw.  This view shows
the silky texture produced by the fine, acicular
crystal growth.  When viewed parallel to the
fibers, Ulexite transmits light in a similar
fashion to fiber optics.  It is this property
that has given rise to it nickname of "TV" stone.

Ulexite NaCaB5O9 -8H2O    (Hydrated sodium
calcium borate)
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In your mineral notes, give the color and luster
for each of the minerals below.
Starter
topaz
galena
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Burnt orange Nonmetallic - glassy (vitreous)
White-silver Metallic
topaz
galena
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Practice Mineral Identification
Use a mineral chart to identify these minerals.
1. This mineral has a hardness of about 6, and
has a metallic luster. It is dark gray to black
in color and has cleavage. It has a black
streak. What mineral is it?
2. This mineral looks very glassy. It could
scratch glass fairly easily. It is a greenish
color with a white streak. I dont think it has
cleavage. What mineral is it?
3. I have a huge piece of this mineral. I
cannot scratch it with my fingernail, but I think
that I scratched it with a penny. The nail
definitely scratched it. It has a glassy, clear
look, and seems to have a lot of flat surfaces.
I dont think it left a streak. What mineral is
it?