Transcript Minerals - TeacherWeb

Chapter 3
Minerals
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Minerals: naturally occurring, inorganic
solids, with definite structure and
composition; made of one or more
elements
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Characteristics of Minerals:
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Formed by natural processes
Inorganic (not formed from life processes)
Solid
Definite chemical composition, can have minor
variations (example: salt is NaCl)
Atoms arranged in a pattern
Structure of Minerals: minerals are in the
form of crystals (a solid in which the atoms are
arranged in repeating patterns)
A.Crystal Systems: Examples of Perfect Crystal
Systems
Cubic
Examples:
Tetragonal
Hexagonal
Cubic-Halite (salt); Platinum
Tetragonal-Zircon; Wulfenite
Hexagonal-Quartz; Corundum
CRYSTAL SYSTEMS are divided into 6 main
groups.- We will look at 3 groups
The first group is the ISOMETRIC.
This literally means “equal measure”
and refers to the equal size of the
crystal axes.
a3
a2
a1
ISOMETRIC - Fluorite Crystals
ISOMETRIC
Basic Cube
HEXAGONAL CRYSTALS
c
a3a
a2
a1
HEXAGONAL Crystal Axes
Three horizontal axes meeting
at angles of 120o and
one perpendicular axis.
These hexagonal CALCITE
crystals nicely show the six sided
prisms
Hexagonal Crystals
TETRAGONAL
CRYSTALS
TETRAGONAL
Two equal, horizontal, mutually perpendicular
axes (a1, a2)
Vertical axis (c) is perpendicular to the
horizontal axes and is of a different length.
c
c
a1
a2
TETRAGONAL Crystal
Axes
a2
a1
This is an Alternative
Crystal Axes
TETRAGONAL
WULFENITE
CRYSTALS
Same crystal seen edge on.
How Minerals Form:
Form from the cooling of hot melted
rock (magma); If it cools fast,
crystals tend to be small; cools slow,
larger crystals tend to form
Form from solutions-as liquid
evaporates, minerals solidify and
form crystals
Major Mineral Groups
Silicates-Made of Silicon, Oxygen, & possibly
other element(s); largest group of minerals
Example: Quartz (SiO2)
Carbonates-Made of Carbon, Oxygen, &
possibly other element(s)
Examples: Calcite (CaCO3); Magnetite (MgCO3)
Most Abundant Elements in
Earth’s Crust:
1. Oxygen
46.6%
2. Silicon
27.7%
3. Aluminum
8.1%
4. Iron
5%
5. Calcium
3.6%
6. Sodium
2.8%
7. Potassium
2.6%
8. Magnesium 2.1%
***All other elements make up 1.5% of the Earth’s
crust.
Physical Properties of Minerals:
Hardness-a measure of
how easily a mineral
can be scratched
***1 is the softest, 10 is the hardest***
Moh’s Scale of Hardness
Sample
Element
Hardness
Talc
1
Gypsum
2
Calcite
3
Fluorite
4
Apatite
5
Feldspar
6
Quartz
7
Topaz
8
Corundum
9
Diamond
10
Common
Objects
Fingernail (2.5)
Copper penny
(3.5)
Iron Nail (4.5)
Glass (5.5)
Steel File (6.5)
Streak Plate (7)
Luster
Describes how light is reflected from a
mineral’s surface
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Metallic
Nonmetallic
dull; pearly; silky; glassy; brilliant; transparent
Waxy
Resinous (looks like freshly broken shellac)
Color
The color seen when looking at the surface
of the mineral; Least reliable property
because many minerals can be many
colors
Example: Sulfur is pale yellow
Streak
The color of the mineral when it’s broken up in
powdered form; Use a porcelain tile to test;
Useful for softer minerals; Minerals with a
hardness greater than 7 do not leave a streak
Example: Gold has a gray streak
The Way a Mineral Breaks
1. Cleavage-When a mineral breaks along
smooth, flat surfaces; Example: Mica
2. Fracture-When minerals break with
rough or jagged edges; Example: Quartz
Special Properties
Unusual or unique qualities; Examples:
Magnetite is magnetic, Calcite has optical
qualities, Jade has a bell-like ring when
tapped, Halite has a salty taste, and Sulfur
smells like rotten eggs
Uses of Minerals
Gems-Highly prized minerals because they
are rare and considered beautiful; the
difference in a gem and the common
form of a mineral can be slight
Ores-contain useful substances that can be
mined for a profit
Examples:
Bauxite contains Aluminum
Hematite contains Iron
Sphalerite contains Zinc
Chalcopyrite contains copper
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Strip Mining-Removing ore by digging at
Earth’s surface; usually results in a huge
pit
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Land Reclamation- mining companies
are required to return soil and rock to
open pit and cover it with topsoil then
plant trees and grass
Asbestos-a mineral with threadlike, flexible
fibers used as insulation and as fire
protection; has been shown to cause
lung diseases including lung cancer
EPA (Environmental Protection Agency)requires school officials to inspect
buildings every six months; flaking
asbestos must be removed or sealed
over
Minerals can contain other useful elements.
1.Elements must be refined, or purified, from ores
2. Some elements dissolve in fluids, travel through
weaknesses in rocks, and in those weaknesses
form mineral deposits called vein mineral
deposits
3. Titanium is useful element derived from the
minerals limonite and rutile