Lecture 1
INTRODUCTION AND MINERALS
INTRODUCTION
Geology
Geology is the study of the Earth. It is divided
into physical and historical geology.
1.
1.
Physical geology examines the materials composing the Earth and seeks to
understand the processes that operate
beneath and upon the surface.
2.
2.
Historical Geology
examines the origin of the Earth and the development of the planet through its
4.6 billion year history.
Four Earth Spheres
Hydrosphere is the dynamic mass of water that is
on the move, evaporating from the oceans to the atmosphere, precipitating back
to the land , and running back to the ocean again.
1.
1.
The oceans
cover 71% of the earth's surface.
2.
2.
The oceans account for 97% of the Earth's water.
3.
3.
Only 3% of the Earth's water is considered fresh water (potential
drinking water).
Atmosphere is very thin compared to the Earth's
diameter and it provides us with the air we breathe and protects us from the
sun's heat and UV radiation.
Biosphere includes all life on Earth and is
concentrated near the surface in a zone that extends from the ocean floor
upward for several kilometers into the atmosphere.
Lithosphere is about 100 km thick and it includes
the entire crust as well as the uppermost mantle. The lithosphere behaves like
a rigid solid.
Structure of the Earth
The Earth is divided into the core, mantle, and
crust.
The core is divided into 2 sections totaling in
thickness of 3486 km.
1.
1.
The inner core is solid consisting of iron and nickel.
2.
2.
The outer core is liquid.
The mantle is a rocky layer located below the
crust and has a thickness of about 2885 km. Its composed of peridotite, an iron
and magnesium rich igneous rock. The mantle can be divided into 3 zones based
on physical characteristics:
1.
1.
Lower mantle is solid and forms most of the volume of the Earth’s interior.
2.
2.
Asthenosphere surrounds the lower mantle and behaves plastically. Flow
of material occurs very slowly and partial melting in this zone generates
magma.
3.
3.
Upper mantle is solid and surround the asthenosphere.
The crust is a very thin outer layer consisting of
oceanic and continental material. It is about 5-40 km thick. Oceanic crust is
denser than continental crust. Thus, the oceans serve as basins for the
accumulation of sea water. Continental crust is composed of aluminum and silicon
rich rocks (granite), while oceanic crust is composed of basaltic rocks.
The lithosphere is composed of the upper mantle
and crust.
Geologic Time
Scale is used to describe the time the Earth has been in existence. The
geologic time scale is divided into Eons, Eras, Periods and Epochs. The bottom
of the scale shows the older rocks and the top shows the more recent rocks.
Eons
- Precambrian (Pre-archean, Archean, and
Proterozoic)
- Phanerozoic
ERAS
- Paleozoic
- Mesozoic
- Cenozoic
PERIODS
- Cambrian
- Ordovician
- Silurian
- Devonian
- Mississippian
- Pennsylvanian
- Permian
Epochs
- Paleocene
- Eocene
- Oligocene
- Miocene
- Pliocene
- Pleistocene
- Recent
MINERALS
General Mineral Information
A mineral is a naturally occurring inorganic solid
that has a definite chemical structure, which gives it a unique set of physical
properties.
A mineral
should exhibit the following characteristics:
1.
1.
be naturally occurring, not human made;
2.
2.
be inorganic, never was alive;
3.
3.
be solid;
4.
4.
have a definite chemical structure;
5.
5.
posses physical properties, such as crystal form, luster, etc.
Minerals are the building blocks
of rocks, and rocks are composed of one or more minerals.
Composition and Structure of Minerals
Minerals are composed of chemical elements, such
as those shown on the Periodic
Table of Elements.
Chemical elements combine to form minerals, and
atoms , which are the smallest particle of matter has all the characteristics
of an element. Atoms are made up of the following:
1.
1.
The nucleus is the part of the atomic structure that contains protons (positive
charged particles) that are very dense and neutrons (neutral charge) that are
equally dense.
2.
2.
Orbiting the nucleus are electrons, which have negative charge.
3.
3.
The atomic number represents the number of protons in an atom nucleus.
Elements combine with each other to form complex
mineral compounds. A compound is composed of two or more elements bonded
together in definite proportions.
When atoms combine chemically they either gain,
lose, or share electrons with another atom. When an atom gains an electron, it
becomes negatively charged, because it has more electrons than protons. When an
atom loses an electron, it becomes positively charged, because it has more
protons than electrons. Atoms that either loose or gain an electron are said to
be ions.
The mass number is the sum of the neutrons and
protons in the nucleus.
Atoms of the same element always have the same
number of protons, but may have different number of neutrons. This is called an
isotope.
Physical Properties of Minerals
Crystal Form is the external expression of a
mineral's internal orderly arrangement of atoms.
1.
1.
In a crystal, the atoms are arranged in a definite geometric pattern
that is repeated over and over again.
2.
2.
The study of crystals is called crystallography.
Luster is the appearance or quality of light
reflected from the surface of a mineral. Minerals that look like metals,
regardless of their color have metallic luster. Minerals with nonmetallic
luster are described by various adjectives, such as:
o
o
vitreous- glassy looking;
o
o
pearly- looks like mother of pearl
o
o
adamantine- has a hard diamond brilliance
o
o
silky- looks like silk
o
o
resinous- looks like tree sap, amber, sulfur
o
o
earthy- dull appearance, looks like dirt
Color is an obvious feature of a mineral, but it
is often an unreliable property, due to chemical impurities (e.g., iron or
sulfur) that may alter the color of a mineral.
Streak is the color of a mineral in its powdered
form, which is more reliable than color for mineral identification. Streak is
obtained by rubbing the mineral across a piece of hard unglazed porcelain
(streak plate). Streaking helps to somewhat eliminate the effects of
impurities.
Hardness is the measure of the mineral's
resistance to abrasion or scratching. This property is determined by rubbing
the mineral to be identified against another mineral of known hardness, from
Mohs Scale of Hardness.
o
o
Mohs scale of hardness consists of 10 minerals.
o
o
The minerals are arranged from 1 to 10, with 1 being the softest and 10
the hardest.
o
o
Mohs Scale of Hardness is represented by the following:
1.
1.
Talc
2.
2.
Gypsum
3.
3.
Calcite
4.
4.
Fluorite
5.
5.
Apatite
6.
6.
Orthoclase
7.
7.
Quartz
8.
8.
Topaz
9.
9.
Corundum
10.
10. Diamond
Cleavage is the tendency of a mineral to cleave or
break along planes of weak bonding. Cleavage is described by the number of
planes exhibited and the angles at which they meet. Some examples of cleavage
are:
·
·
Cleavage in one direction
·
·
Cleavage in two directions at right angles
·
·
Cleavage in three directions at right angles
·
·
Cleavage in three directions not at right angles
·
·
Cleavage in four directions
·
·
Cleavage in six directions
Minerals that do not exhibit cleavage when
broken, exhibit fracture. Fractures are often rough, splintery surfaces. Except
for conchoidal fracture, which are smooth curved surfaces like those seen in
broken glass.
Specific Gravity compares the weight of a mineral
to the weight of an equal volume of water. For example, if a cubic centimeter
of mineral has a specific gravity of 3, then the mineral weighs 3 times as much
as a cubic centimeter of water. The formula for specific gravity is the weight
of the mineral in air divided by the weight of the mineral in air minus the
weight of the mineral in water. Specific gravity is unitless. The various
weights of the mineral, in air and in water are obtained using a Jolly Balance.
Silicates
Silicon and oxygen (the most common elements on
the Earth's crust) combine to form silicates. Silicates have a silicon-oxygen
tetrahedron structure.
The silicon-oxygen tetrahedra have four oxygen
atoms surrounding a smaller silicon atom.
The tetrahedra can be joined into chains, sheets,
and 3 dimensional networks by sharing oxygen atoms. For example, olivine is
composed of a single tetrahedron, pyroxene group of single chains, amphibole
group of double chains, micas of sheets, and feldspars and quartz of 3 dimensional
networks.
Other Mineral Groups
·
·
Oxides
·
·
Sulfides
·
·
Sulfates
·
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Native Elements
·
·
Halides
·
·
Carbonates