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Advance Placement
Rocks and Minerals:
Classification and Usage
Rocks and Minerals
Objectives
Materials
Introduction
After this lab you should be able to do the following:
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Understand and perform different methods of classifying rocks and minerals.
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Identify important common rocks and minerals.
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Identify common uses of rocks and minerals.
Materials for this lab are:
Mineral dichotomous keys
Mineral Samples
Glass plate
steel nail
Copper penny
magnet
Hand lens
hydrochloric acid
Internet
Streak Plates
Rock samples
Water
Gloves
First, before we begin, we must understand what a mineral is. A mineral is a
naturally occurring, inorganic, solid, with a definite chemical composition
and crystal structure. Now that you understand what a mineral is, lets discuss the
methods we can use to identify them. Minerals have certain physical properties
(characteristics) that help us to identify them, such as:
Color
Although color is the most obvious, it is the least reliable. For example specimens of the
mineral- calcite are always the same color as Sulfur, and Pyrite.
Streak
When an unknown mineral is rubbed against a piece of unglazed porcelain (a.k.a.-streak
plate) it may produce a colored line. This color will help to determine the minerals
identification. This test is very useful for Hematite and Limonite. Many times a sample
does not leave a color streak however, or is harder than the streak plate. Examples are
the minerals Galena and Hematite. Both have metallic luster and seem heavy for their
relative sizes, but Hematite has a red brown streak.
Fracture and Cleavage
These terms describe the way a mineral breaks. If a mineral fractures, it breaks along
rough edges. If it cleaves, then it breaks along smooth, flat surfaces. Some rocks also
have a type of cleavage called slaty cleavage. This is not the same type of cleavage
exhibited by a mineral. Cleavage found in minerals is the result of the way the chemicals
bond together, but in rocks, it is the result of the way the minerals align themselves
parallel to one another.
When some minerals fracture, they appear to break along long curved surfaces (that
look like a shell. This type of fracture is known as conchoidal fracture and Quartz and
the igneous rock Obsidian will demonstrate this type of fracture. The rough, irregular
breaking is known as hackly fracture.
Hardness
This is how resistant a mineral is to being scratched. We use the Mohs scale to classify a
given minerals hardness. If we have a sample that we can scratch with Fluorite, but not
with Gypsum, we can predict that the samples hardness is around 3. But if you forgot
your hardness scale minerals at home (and don't we all sometimes) we can use a simple
field method. The technique used is rather similar. All you do is try to scratch the
unknown mineral with various items, such as a fingernail (hardness of about 2.5), a
penny (3), a steel nail (5.5) and a steel file (7). The item that first scratches the
unknown is harder than the unknown so now you must estimate. Below is the Mohs
Scale.
MOHS SCALE OF HARDNESS
MINERAL
HARDNESS
TALC
1
GYPSUM
2
CALCITE
3
FLUORITE
4
APATITE
5
FELDSPAR
6
QUARTZ
7
TOPAZ
8
CORUNDUM
9
DIAMOND
10
Luster
The way a mineral reflects light. Does your mineral appear to be a metal (metallic
luster)? Or does it look like a nonmetal (nonmetallic luster)? There are several other
words used to describe luster.
Crystal form
The way the outside of this mineral looks is an expression of the arrangement of its
atoms. This external expression is known as a crystal. Its crystal structure is the result
of regular grouping of atoms that are homogeneous (having the same characteristics
throughout the crystal).
A crystal is a polyhedral form, which means it is a geometric solid. It has a specific set of
faces, corners and edges, which is consistent with
the geometric packing of the atoms.
There are 6 basic crystal forms. The form that the
unknown demonstrates is a good clue to its identity.
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. Often,
you may need to resort to this method (until you more fully understand other identifying
traits) to differentiate halite from calcite. You should not use taste unless directed to by
someone with higher knowledge
Specific Gravity
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.
Magnetism
Is a mineral magnetic (try using a compass), or is it attracted by a magnet? This
property is characteristic of Magnetite.
Effervescence
When some minerals are exposed to acids, they begin to fizz. This is a great method
you can use to identify the mineral calcite. You can also use this one to detect the
presence of calcite in rocks.
Birefringence
This is also known as double refraction. Birefringent minerals split the light into two
different rays which gives the illusion of double vision in this Iceland Spar Calcite
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 above
mineral (opal) is demonstrating fluorescence. Also, the mineral Fluorite is often strongly
fluorescent.
Pre-lab Questions 1. Create a list of minerals you know we use.
2. Research quality of precious metals (gold, silver, copper) what useful properties do
they show?
3. Choose three useful properties of minerals from above. In your own words, explain
what you would look for to classify each property.
Procedure
1. You will be provided with 12 sample minerals. Use the properties in the pre-lab to
classify the properties of each minerals. Fill in a chart showing your results.
2. Two similar looking minerals from your twelve will be provided. Use the properties
from above classify each. Explain how you were able to recognize the difference.
Lab Questions
1. For each type of rock, describe how it forms and name an example. Also give the
mineral make-up of that specific rock.

Clastic sedimentary

Biological sedimentary

Chemical sedimentary

Intrusive igneous

Extrusive igneous

Metamorphic
2. Use books or the internet to research uses of each of the following rocks and
minerals. Identify each as a rock or a mineral.
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Barite
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Marble
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Calcite
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Mica
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Coal
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Molybdenum
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Copper
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Potash
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Fluorite
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Sandstone
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Gypsum
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Silver
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Granite
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Sulfur
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Halite
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Talc
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Iron
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Trona
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Limestone
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Ulexite
3. Use the internet to find the mineral(s) important to the following industries
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automobile
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cosmetics
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fireworks
4. What are some reasons that mineral resources are considered valuable.
5. In North Carolina, the following rocks and minerals are mined: Gemstones - Emeralds,
rubies, garnets and more than 300 other varieties, Gold, Crushed stone (aggregate),
Kaolin clay, Olivine, Quartz and feldspar, Peat, Phosphate, Silica sand and quartz,
Spodumene, Talc and pyrophyllite. Use the information you’ve collected to name three
industries that would rely on North Carolina’s minerals.