Minerals

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Chapter 3

• Minerals

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• Minerals naturally occurring, inorganic solids,
  with definite structure and composition made of
  one or more elements
• Characteristics of Minerals
• 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

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• Structure of Minerals minerals are in the form
  of crystals (a solid in which the atoms are
  arranged in repeating patterns)

• Crystal Systems Examples of Perfect Crystal
  Systems

Cubic Tetragonal
Hexagonal
Examples Cubic-Halite (salt) Platinum
Tetragonal-Zircon Wulfenite
Hexagonal-Quartz Corundum
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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.
ISOMETRIC - Fluorite Crystals
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HEXAGONAL CRYSTALS
c
a
a3
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
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Hexagonal Crystals
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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.
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• TETRAGONAL CRYSTALS

WULFENITE
Same crystal seen edge on.
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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

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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)

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Most Abundant Elements in Earths 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
  Earths crust.

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Physical Properties of Minerals

• Hardness-a measure of how easily a mineral can be
  scratched

1 is the softest, 10 is the hardest 1 is the softest, 10 is the hardest 1 is the softest, 10 is the hardest
Mohs Scale of Hardness Mohs Scale of Hardness Mohs Scale of Hardness
Sample Element Hardness Common Objects
Talc 1 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Gypsum 2 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Calcite 3 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Fluorite 4 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Apatite 5 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Feldspar 6 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Quartz 7 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Topaz 8 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Corundum 9 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
Diamond 10 Fingernail (2.5) Copper penny (3.5) Iron Nail (4.5) Glass (5.5) Steel File (6.5) Streak Plate (7)
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Luster

• Describes how light is reflected from a minerals
  surface
• Metallic
• Nonmetallic
• dull pearly silky glassy brilliant
  transparent
• Waxy
• Resinous (looks like freshly broken shellac)

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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

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Streak

• The color of the mineral when its 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

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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

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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

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• 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

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• 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 Earths
  surface usually results in a huge pit
• Land Reclamation- mining companies are required
  to return soil and rock to open pit and cover it
  with topsoil then plant trees and grass

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• 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

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• 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