Minerals!

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Minerals!

• The Building Blocks of Rocks

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Minerals

• All minerals are made up of single elements or
  compounds
• Element an element is made up of atoms, and
  cannot be broken down into a simpler substance
• Compound a compound contains 2 or more kinds of
  atoms that are bonded (chemically joined)
  together
• Atom an atom is the smallest part of an element
  it has all of the properties of the element,
  but cannot be seen even with tools!

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Definition of a Mineral must exhibit ALL of
these traits!

• Naturally occurring synthetic substances are
  NOT minerals
• Inorganic cannot form as a result of
  plant/animal activities (pearls and coal are NOT
  minerals)
• Solid
• Definite chemical composition (they are composed
  of distinct elements or combinations of elements)
• (Take a look at the last page of your ESRT!)
• Internal arrangement of atoms gives it a
  crystalline structure
• Definite set of physical properties

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Quartz and the Silicon Oxygen tetrahedron
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MINERAL FAMILIES

• Minerals can be classified according to their
  chemical compositions page 16 of ESRT
• OXIDES composed of oxygen and 1 other element
  (not Si) example is Hematite
• SULFIDES composed of sulfur and 1 other element
  example is Galena
• CHLORIDES (Halides) composed of chlorine and 1
  other element example is Halite
• CARBONATES composed of 1 or more metals CO3
  (carbonate) example is Calcite
• SULFATES 1 or more metals SO4 (sulfate)
  example is Selenite gypsum
• SILICATES 1 or more metals Silicon and Oxygen
  example is Quartz

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Properties of Minerals for ID!

• These are used to identify minerals in labs or in
  the field!
• Color
• Luster
• Streak
• Hardness
• Breakage Pattern (Cleavage or Fracture)
• Density/Specific Gravity
• Crystal Shape
• Special properties such as odor, acid reaction,
  magnetism, taste (salty), double refraction,
  striations
• ENR Diaphaneity, Tenacity

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Color

• Color is a useful property only for some minerals
• For most minerals, however, color is NOT a useful
  ID tool why?
• 1) many minerals come in different colors
• 2) one color, such as white, can be seen in many
  different minerals
• But, color can be used to ID certain minerals
  that usually exhibit only 1 color (such as
  sulphur, which is yellow)

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Sulphur
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These are ALL the same mineral!
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These are different minerals!
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So, is color useful?

• No!!
• Well, sometimes..
• But it sure makes looking at minerals a LOT more
  interesting, yo!

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Luster

• The way light shines or glares off the surface of
  minerals
• This is better than color in mineral ID
• This is a fairly subjective property
• You need to become familiar with some terms

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Luster main properties

• Metallic looks like metal in the way it reflects
  light examples are galena or pyrite (like
  polished metal) Bling
• Sub-metallic (like unpolished metal) - Blung
• Non-metallic does not look like polished metal,
  so other terms are needed!

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Galena
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Pyrite Fools Gold!
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ENR- Types of Non-Metallic Luster

• Vitreous glassy looking, like quartz
• Silky umlike silk
• Waxy/Resinous dull shine like candle wax or
  resin like sulphur
• Adamantine gives off a glare at a certain
  angle, like a diamond
• Dull/Earthy no shine at all, like bauxite
• Pearly - looks like a pearl when light reflected
  off it, like garnet or opal
• Greasy like soap (talc)

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Streak

• The color of the mineral in powder form when its
  rubbed against a porcelain plate (called a streak
  plate)
• Most minerals display only one streak color
• Hematite always has a reddish brown streak
• Sulphur has a yellow streak
• Sphalerite has a yellow streak
• Magnetite has a black streak

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Streak
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Hardness

• The minerals resistance to being scratched
• We use Mohs Hardness Scale to determine a
  minerals hardness
• This scale uses 10 index minerals with hardness
  ranging from 1 (least hard) to 10 (hardest)

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Mohs Hardness Scale
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Visual Mohs
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Mohs
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How do we use Mohs?
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Breakage Pattern

• Cleavage the tendency of a mineral to break
  along planes of weakness
• Fracture no definite planes of weakness, just
  breaks irregularly

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Crystal Shape

• Crystal shape can vary, and can be difficult to
  recognize

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Cleavage

• Tendency to split along flat surfaces (planes)
  where the chemical bonds are weak
• Can be spotted when light reflects off an entire
  surface simultaneously
• Can be in several directions at varying angles

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Cleavage directions/angles
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Fracture

• Tendency to break WITHOUT cleavage, randomly
• Can still exist in minerals that show cleavage in
  other directions though
• ENR
• Types
• Conchoidal fracture pattern resembles a conch
  shell
• Fibrous looks like fibers
• Uneven looks uneven

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Fracture
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Density/Specific Gravity

• Every mineral has a certain density, but only
  sometimes is it useful for ID!
• A great example is the hefty mineral Galena

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Acid Reaction

• Minerals in the carbonate family (CO3) will react
  to HCl and will release CO2 bubbles (called
  effervescence)

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ENR - Tenacity

• Resistance to crushing, bending, etc.
• See lab packet for types

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ENR - Diaphaneity

• How light is transmitted through a mineral (or
  not)
• Transparent full transmission of image
• Translucent hazy light but no image
• Opaque zero, zilch, nada transmission

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Special properties

• Magnetism mineral is magnetic, like Magnetite
• Taste (salty) mineral tastes like salt, because
  thats what it is Halite
• Double refraction mineral will transmit an
  image and will double it! Iceland Spar (a type of
  calcite) will do this.
• Striations tiny grooves on a cleavage plane
  (Plagioclase Feldspar)
• SEE page 16 of the ESRT, and look in the
  DISTINGUISHING CHARACTERISTICS column

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