Transcript Section 4.2 : Identifying Minerals Mineral Identification

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OBJECTIVES:
• Define a mineral.
• Describe how minerals
form.
• Identify the most common
elements in Earth’s crust.
VOCABULARY
mineral , crystal, magma and silicate
Facts about Minerals:
• Earth’s crust is composed of about 3000 minerals.
• Minerals play a role in forming rocks and shaping
Earth’s crust
• Calcite is the mineral that forms the 2 million
limestone blocks that make up the Great Pyramid
in Egypt.
• Calcite is the primary mineral in the marble that
makes up the Parthenon in Greece.
• Kingdoms have waged wars over silver and gold.
?
Answer:
What is a
Mineral?
A mineral is a naturally
occurring, inorganic solid
with a specific chemical
composition and a
definite crystalline
structure.
Let’s Examine this definition:
• Naturally occurring and Inorganic.
Naturally occurring – means it is formed in nature.
Inorganic – means that it doesn’t contain carbon and
that it was never a living breathing organism.
Using your computers find the chemical formula for
table salt (halite) and sugar (sucrose). Which of
these is considered a mineral and which is not?
Let’s Examine this definition:
• Solids with Specific Compositions.
Solids– have a definite shape and a definite volume.
Specific Compositions – Each mineral has a chemical
composition
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Let’s Examine this definition:
• Definite Crystalline Structure.
The atoms in minerals are arranged in a repeating
geometric pattern. Solids with repeating geometric
patterns are called crystals.
Tetragonal
Cubic
Orthorhombic
Hexagonal
Triclinic
Monoclinic
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Minerals From Magma:
• Minerals can form from the cooling of magma.
Magma – the molten material found beneath Earth’s
surface.
If the magma cools slowly (within the
Earth’s interior), the atoms arrange
themselves to form large crystals.
If the magma reaches air or water and
cools quickly (Earth’s exterior), then
the atoms form small crystals.
?
Of the 3000
known minerals,
how many make
up 90% of the
Earth’s crust?
Answer:
10
?
What is the
most common
element in
Earth’s crust?
Fact: About 90 known
elements are found in
Earth’s crust.
Answer:
Oxygen
• Minerals are compounds made up
from a combination of elements.
• Minerals that contain Oxygen and
Silicon (and usually one or more
other elements are known as
Silicates.
• Silicates make up about 96% of
the minerals found in Earth’s
crust.
• The most common silicates are:
feldspar and quartz.
Silicates form a pyramid shaped
structure called a tetrahedron.
• Silica tetrahedrons can combine
in many ways, including:
• Single Chains
• Double Chains
• Sheets
Other Mineral Groups:
• Carbonates
Carbonates are minerals composed of one or
more metallic elements with the carbonate
“compound” -CO3
Examples: Calcite, Dolomite, and rhodochrosite.
(Carbonates are primarily found in limestone,
coquina, and marble.) Some carbonates are known
for their distinctive colors.
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Other Mineral Groups:
• Oxides
Oxides are compounds of oxygen and metal.
Examples: Hematite, Fe2O3, and magnetite, Fe3O4,
are common oxides and good sources of iron.
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Other Mineral Groups:
• Oxides
Oxides are compounds formed from a metal
and oxygen.
Examples: Hematite Fe2O3
Magnetite Fe3O4.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
Question: Why do you think it’s best to have more than
one test to identify a mineral?
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
1 – COLOR (This is the least reliable identification test.)
Some minerals can be found in several colors. “Trace”
elements can cause color variations among minerals.
(See the bottom of page 84 for an example of color variations
in the mineral quartz.)
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
2 – Luster
The way that a mineral reflects light is referred to as luster.
Luster is often described as metallic (shiny) or nonmetallic
(dull).
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
3 – Texture
Texture describes how a mineral feels to the touch.
Example: Smooth, rough, greasy, soapy, or glassy.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
4 – Streak
Scratching a mineral against an unglazed porcelain plate will
often leave an identifying powder or “streak”.
Streak is the color left by a mineral when it is broken up.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
5 – Hardness
Hardness is a measure of how easily a mineral can be
scratched.
German geologist Frederick Mohs developed a scale for
mineral hardness that is still used today.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
6 – Cleavage and Fracture
A mineral that splits evenly and evenly along one or more
planes is said to have “cleavage”. Minerals that break in a
rough or jagged manner are said to have “fracture”.
Minerals that have cleavage tend to break where the bonds
between atoms are weak.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Geologist use several test to identify minerals based
upon the minerals chemical and physical properties.
7 – Density and Specific Gravity
The density of a substance if found by it’s mass/volume ratio.
Density = mass / volume.
Specific Gravity is a comparison of a substances density to
the density of water.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Sometimes “special properties” can be used to
identify minerals:
Iceland Spar – Refracts (bends) light in two directions.
Magnetite - Attracts metals
Sphalerite – Smells like rotten eggs when it’s scratched.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Ores
– An ore is a mineral that contains a useful
substance that can be mined at a profit.
– Examples of ores include Hematite, which
contains the element iron and bauxite, which
contains the element aluminum.
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Section 4.2 : Identifying Minerals
• Mines
– Ores are removed by underground mining or from large,
open-pit mines.
– When a mine is excavated, unwanted rock and dirt, known
as waste material, are dug up along with ore.
– If the cost of separating the waste material becomes higher
than the value of the ore itself, then the mineral will no
longer be classified as an ore because it would no longer be
economical to mine it.
– The classification of a mineral as an ore may also change if
the supply of or demand for that mineral changes.
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Section 4.2 : Identifying Minerals
• Mineral Identification
Gems
Gems are valuable minerals that are prized for
their rarity and beauty.
• Gems such as rubies, emeralds, and diamonds are
cut, polished, and used for jewelry.
• In some cases, the presence of trace elements can
make one variety of a mineral more colorful and thus
more prized than other varieties of the same mineral.
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