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CE301-Lecture-4-Mineralogy

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Mineralogy
Engr. Heber John De Vera
CHAPTER OBJECTIVES:
At the end of this lecture, the student will be
able to:
• Describe what a mineral is, and its defining
properties.
• Identify minerals based on their physical
characteristics or properties.
• Sort minerals into the correct mineral class.
• Describe
minerals.
how
melted
rock
produces
• Describe how rock produces different
minerals.
• Explain how minerals form from solutions.
THE BASICS OF MINERALOGY
• In general terms, a mineral is an element or
chemical compound that is normally crystalline
and that has been formed as a result of
geological process (E.H. Nickel, 1995).
• A mineral is a naturally occurring combination of
specific elements arranged in a particular
repeating three-dimensional structure or lattice.
• Minerals are naturally occurring, inorganic solids
with a definite composition and a crystal lattice
structure.
Although thousands of minerals in the earth have
been identified. Just ten minerals make up most of
the volume of the earth’s crust – plagioclase, quartz,
orthoclase, amphibole, pyroxene, olivine, calcite,
biotite, garnet, and clay.
PHYSICAL PROPERTIES OF MINERALS
To be considered a mineral, an earth material must meet these
requirements:
• It’s solid: Minerals are solid at the temperature of earth’s surface.
• Usually, it’s inorganic: Most minerals are inorganic, meaning they
are not alive or the remains of a live organism. However, some
animals create mineral shells. In this case, when the animal dies
and these shells remain, the shell materials can be considered
minerals.
• It has an orderly structure: When atoms combine
to form minerals, they do so in an organized way
that forms a geometric pattern called a crystal.
Earth materials that form without this orderly
crystalline structure are described as amorphous
or glassy and are not minerals.
MINERALS
To be considered a mineral, an earth material must meet these
requirements:
• It is naturally occurring: True minerals are found in nature. Humans
have the technology to combine atoms into crystals in a lab, but
the manmade crystals are not considered minerals.
• It has specific chemical composition: Each mineral has a defined
chemical composition: a combination of elements that creates
its particular crystalline structure.
PHYSICAL PROPERTIES OF MINERALS
Minerals can be identified by their physical characteristics. The
physical properties of materials are related to their chemical
composition and bonding.
• Color – Color is often useful but not relied upon. Different minerals
may be the same color. Some minerals come in many different
color.
PHYSICAL PROPERTIES OF MINERALS
• Luster – It describes the reflection of light off
a mineral’s surface. It is how the surface of a
mineral reflects light. One simple way to
classify luster is based on whether the
mineral is metallic or non-metallic. Standard
names for luster include metallic, glassy,
pearly, silky, greasy, and dull.
•
Metallic luster means opaque, translucent and
have the appearance of polished metal.
•
Glassy luster is the most common of the
nonmetallic lusters and means the surface of the
mineral reflects light like glass.
•
Pearly luster refers to a subtle iridescence or color
play in reflected light.
•
Silky luster means reflecting light with a silk-like
sheen.
PHYSICAL PROPERTIES OF MINERALS
Six Different Types of Non-Metallic Luster
Luster
Appearance
Adamantine
Sparkly
Earthy
Dull, clay like
Pearly
Pearl-like
Resinous
Like resins, such as tree saps
Silky
Soft-looking with long fibers
Vitreous
Glassy
PHYSICAL PROPERTIES OF MINERALS
• Streak – is the color of a mineral’s powder. Streak is a more reliable
property than color because it does not vary. Minerals that are the
same color may have a different colored streak. Some minerals,
such as the quarts do not have streak.
• Specific Gravity – Density describes how much matter is in a certain
amount of space. The specific gravity of a substance compares its
density to that of water. Substances that are denser have higher
specific gravity.
• Hardness – is the strength with which a mineral resists its surface
being scraped or punctured. In working with hand samples without
specialized tools, mineral hardness is specified by the Mohs
hardness scale.
PHYSICAL PROPERTIES OF MINERALS
The Mohs hardness scale is based on 10 reference minerals, from talc
the softest, to diamond the hardest.
Hardness
Index Minerals
Hardness
Index Minerals
1
Talc
6
apatite
2
gypsum
7
quartz
3
calcite
8
topaz
4
fluorite
9
corundum
5
feldspar
10
diamond
PHYSICAL PROPERTIES OF MINERALS
• Cleavage – is the tendency of mineral to break
along a certain plains to make smooth surfaces.
A mineral that naturally breaks into perfectly flat
surfaces is exhibiting cleavage. A cleavage
represents a direction of weakness in the crystal
lattice.
• Fracture – is a break in a mineral that is not along
a cleavage plane. Fracture is not always the
same in the same mineral because fracture is
not determined by the structure of the mineral.
• Crystal Shape – The shape of a crystal follows the
symmetry of its crystal lattice. There are two
complicating factors to remember: minerals do
not always form nice crystals when they grow
and a crystal face is different from a cleavage
surface.
PHYSICAL PROPERTIES OF MINERALS
• Other identifying characteristics of minerals
Property
Description
Fluorescence Mineral glows under ultraviolet light
Magnetism
Mineral is attracted to a magnet
Radioactivity Mineral gives off radiation that can be measured with
Geiger counter
Reactivity
Bubbles form when minerals is exposed to weak acid
Smell
Some minerals have a distinctive smell
Taste
Some minerals taste salty
CLASSES OF MINERALS
Minerals are classified according to their chemical properties. Except
for the native element class, the chemical basis for classifying
minerals is the anion, the negatively charged ion that usually shows
up at the end of the chemical formula of the mineral. The major
classes of minerals are:
• Silicates
• Sulfides
• Carbonates
• Oxides
• Halides
• Sulfates
• Phosphates
• Native Elements
CLASSES OF MINERALS
• Silicates – Based on the polyatomic anion, (SIO4)4-, which has a
tetrahedral shape. Most minerals in the earth’s crust and mantle
are silicate minerals. All silicate minerals are built of silicon-oxygen
tetrahedra (SIO4)4- in different bonding arrangements which create
different crystal lattices.
• In nesosilicates, also called island silicates, the silicate
tetrahedra are separate from each other and bonded
completely to non silicate atoms.
• In sorosilicates or paired silicates, the silicate tetrahedra are
bonded in pairs.
• In cyclosilicates, also called ring silicates,
silicate tetrahedra are joined in rings.
• In phyllosilicates or sheet silicates, the
tetrahedra are bonded at three corners to
form flat sheets.
CLASSES OF MINERALS
• In single-chain inosilicates the silicate tetrahedra are bonded in
single chains.
• In double-chain inosilicates the silicate tetrahedra are bonded
in double chains.
• In tectosilicates, also known as framework silicates, all corners of
the silicate tetrahedra are bonded to corners of other silicate
tetrahedra, forming a complete framework of silicate
tetrahedra in all directions.
• Sulfides - These are based on the sulfide ion, S2–. Some sulfides are
mined as sources of such metals as zinc, lead, copper, and tin.
• Carbonates - These are based on the carbonate ion, (CO3)2–.
Calcite, CaCO3, and dolomite, CaMg(CO3)2, are carbonate
minerals. Carbonate minerals tend to dissolve relatively easily in
water, especially acid water, and natural rainwater is slightly acid.
• Oxides - These are based on the oxygen anion, O2–. Examples
include iron oxides such as hematite, Fe2O3 and magnetite, Fe3O4,
and pyrolusite, MgO.
CLASSES OF MINERALS
• Sulfates - These have the polyatomic sulfate ion, (SO4)2–, as the
anion. Anhydrite, CaSO4, is a sulfate.
• Phosphates - These have the polyatomic phosphate ion, (PO4)3–,
as the anion. Fluorapatite, Ca5(PO4)3F, which makes your teeth
hard, is a phosphate mineral.
• Native Elements - These are made of nothing but a single element.
Gold (Au), native copper (Cu), and diamond and graphite, which
are made of carbon, are all native element minerals. Recall that a
mineral is defined as naturally occurring. Therefore, elements
purified and crystallized in a laboratory do not qualify as minerals,
unless they have also been found in nature.
HOW TO IDENTIFY MINERALS
First, you need good light and a hand lens or
magnifying glass. A hand lens is a small, double-lens
magnifying glass that has a magnification power of
at least 8x and can be purchased at some
bookstores and nature stores. Minerals are identified
on the basis of their physical properties.
When identifying a mineral, you must:
1.Look at it closely on all visible sides to see how it
reflects light
2.Test its hardness
3.Identify its cleavage or fracture
4.Name its luster
5.Evaluate any other physical properties necessary to
determine the mineral’s identity
FORMATION OF MINERALS
Minerals form under an enormous range of geologic conditions.
Minerals can form from volcanic gases, sediment formation, oxidation,
crystallization from magma, or deposition from a saline fluid.
Formation from Hot Materials
A rock is a collection of minerals. Many minerals start out in liquids that
are hot enough to melt rocks. Magma is melted rock inside Earth, a
molten mixture of substances that can be hotter than 1,000°C.
Magma cools slowly inside Earth, which gives mineral crystals time to
grow large enough to be seen clearly.
When magma erupts onto Earth’s surface, it is called lava. Lava cools
much more rapidly than magma when it is below the surface. In a
cooling lava, mineral crystals do not have time to form and are very
small. The chemical composition will be the same as if the magma
cooled slowly.
Existing rocks may be heated enough so that the molecules are
released from their structure and can move around. The molecules
may match up with different molecules to form new minerals as the
rock cools. This occurs during metamorphism.
FORMATION OF MINERALS
Formation from Solutions
1. Minerals from Salt Water
Water can only hold a certain amount of dissolved minerals
and salts. When the amount is too great to stay dissolved in the
water, the particles come together to form mineral solids, which sink.
Halite easily precipitates out of water, as does calcite.
2. Minerals from Hot Underground Water
Magma heats nearby underground water, which reacts with the
rocks around it to pick up dissolved particles. As the water flows
through open spaces in the rock and cools, it deposits solid minerals.
The mineral deposits that form when a mineral fills
cracks in rocks are called veins.
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