Rocks

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Rocks Minerals

• Geology at its finest

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Minerals

• Minerals can be defined by the 5 properties that
  the must possess.
• 1) Inorganic a mineral must not be alive or
  formed from once living material. Coal would NOT
  be a mineral because it was once alive (organic)
• 2) Occurs naturally in the earth. Steel and
  cement would not be minerals because they are man
  made.
• 3) Always a solid.
• 4) Has a definite chemical composition. The same
  atoms in the same ratios.
• 5) The atoms form a repeated pattern called a
  crystal

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Minerals (Cont.)

• There are more than 2000 minerals.
• Minerals can be made of a single element.
• Ex. Gold, Copper, Iron, Sulphur.
• Minerals may be a compound.
• Ex. Halite (salt)

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Mineral Formation

• Most minerals form from cooling magma or lava.
• Some minerals form from mineral particles
  dissolved in a liquid that evaporates.
• Calcite forms this way.
• The rate of mineral formation determines the size
  of the crystal in the mineral
• When a mineral forms quickly the mineral crystal
  will be small.
• When a mineral forms slowly the mineral crystal
  will be large.

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Exceptions to the 5 criteria rules of minerals

• Diamonds.
• Diamonds ARE considered minerals although they
  form from coal which is organic and not
  considered a mineral.
• Obsidian
• Obsidian is considered a mineral even though it
  cools so quickly that crystals dont form at all.

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Geodes

• A geode is a rock with a hallow interior lined
  with mineral crystals.
• Most geodes contain quartz crystals.

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Composition of Minerals

• The 2 most common elements that make up minerals
  are silicon and oxygen.
• The next 6 most common elements are aluminum,
  calcium, iron, magnesium, potassium, sodium.
• Even though these 8 are the most common elements
  in minerals, only 100 are made of combinations of
  these elements and fewer than 20 are found
  everywhere.
• Many minerals are rare.

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Identifying Minerals

• There are 8 ways to help determine what minerals
  are.
• Color
• Luster
• Hardness
• Streak
• Density (specific gravity)
• Crystal Shape
• How it breaks (Cleavage or Fracture)
• Special Properties

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Color

• Obvious, but not always definitive.
• Sulfur is (almost) always yellow, and there are
  a few others, but not many minerals have a fixed
  color.
• Small amounts of impurities can drastically
  change a mineral's color.
• Many minerals share the same color. (Black is
  common)

Sulfur
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Luster

• The quantity and quality of light reflected from
  the surface.(How shiny it is).
• Most are relatively obvious, but some minerals
  can exhibit a range of lusters (ex. Hematite).
• Metallic looks like a metal. Metallic minerals
  are commonly shiny and opaque
• Non-metallic doesn't look like a metal. There
  are many subtle differences in the non-metallic
  lusters, but most are relatively dull, and are
  often transparent to translucent on thin edges.
  (May be called pearly, glassy, earthy, even
  brilliant)

Galena
Asbestos
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Hardness

• Hardness is the resistance of a mineral to
  scratching.
• It does NOT refer to how easily the mineral is
  broken.
• Hardness is a measure of the bonding strength
  between atoms. If these bonds are strong, the
  mineral is not easily scratched. Minerals with
  weaker bonds are more easily scratched. Pencil
  "lead" is softer than paper, so it writes.
• Hardness in minerals can vary due to impurities,
  but is usually definitive. We determine the
  relative hardness of minerals using a scale
  devised by mineralogist Friedrich Mohs. The scale
  assigns hardness to ten common index minerals,
  and is based on the ability of one mineral to
  scratch another.
• Hardness may be relatively determine by the field
  harness scale (1-7)

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Mohs Hardness Scale
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Field Hardness Scale
Often steel files are used to scratch harder
minerals if you cant identify quartz. This would
not work on minerals harder than 7.
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Streak

• The color of the powdered mineral.
• The test is usually performed by scraping the
  mineral across a piece of unglazed porcelain.
• Streak can be definitive. Good examples include
  hematite (always red-brown no matter what form
  it's in) and chromite (distinguished from the
  hundreds of other black minerals by its
  chocolate-brown streak).
• Some minerals dont streak or streak is clear.
  Some have the same color streak.

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Density (Specific Gravity)

• Defined as "the weight of a specific volume of a
  mineral divided by the weight of an equal volume
  of water (at 4C.)"
• Since water is always 1.0, it's the same number
  as density without any units (they cancel).
• This is almost impossible to measure in the
  field, but a rough approximation and be
  determined.

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Crystal Shape
Determined by the number of faces on the
mineral. The shapes often hard to see and require
a microscope
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How the mineral breaks

• How a mineral breaks is determined by its
  internal structure, and is therefore very
  important (and nearly always diagnostic).
  Unfortunately, it can also be the hardest to
  determine (sorry). There are two (2) major
  subdivisions fracture and cleavage.
• Fracture The mineral just breaks, leaving an
  uneven surface. (jagged) Most are irregular but
  there are some special cases (ex the conchoidal
  fractures common to quartz and glass)
• Cleavage The mineral splits along closely spaces
  parallel planes, leaving a mirror surface which
  will flash at you if rotated in the light. Smooth
  and even.

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Special Properties

• Effervescence (the Fizz test) Minerals
  containing calcium carbonate (CaCO3) will
  generally react when exposed to weak acid
  (usually hydrochloric acid (HCl), but even
  vinegar will work). Carbon dioxide (CO2) is
  released and the mineral or rock literally
  "fizzes."
• Magnetism Magnetite is naturally magnetic. Don't
  put a chunk near your computer!
• Taste Some minerals have a distinctive taste.
  Notable examples include Halite (rock salt), and
  Chalcanthite (a copper sulfate - be careful with
  this one!!). I don't generally recommend the
  taste test.
• Smell Some minerals have a distinctive odor.
  Sulfur is a good example.
• Fluorescence comes from mineral fluorite. It
  glows under a UV light.

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Uses of minerals

• Minerals are used for many everyday uses.
• They are often found in ores (rock deposits where
  economically useful minerals are mined for
  profit)
• They must be mined and have impurities removed.
• Sometimes impurities are removed by the process
  of smelting. (metals)
• Can mine both metals and non metals.

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Metals

• Many useful minerals are metals.
• Shiny
• Good conductors
• Malleability (the ability to be hammered into
  thin sheets without breaking)
• Ductility (the ability to be drawn into wires
  without breaking)
• Ex Gold, silver, copper, iron, lead, aluminum,
  ect.

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Non Metals

• NOT good conductors, malleable, ductile or shiny.
• Ex. Sulfur, asbestos, and halite
• Includes Gems (rare, durable and beautiful
  minerals)
• Precious stones rarest and most valuable gems,
• Ex Diamonds, emeralds, rubies and sapphires
• Semiprecious stones- not as rare or valuable
• Ex. Amethyst, garnet, opal, turquoise, zircons.

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Rocks

• Solids made of one or more minerals.
• All minerals are rocks, but not all rocks are
  minerals
• The study of rocks is called Petrology
• The word petrology comes from the apostle Peter.
  Matthew 1618

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Types of Rocks

• There are 3 main types of rock.
• Igneous
• Sedimentary
• Metamorphic

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Igneous Rocks

• Igneous rocks are called fire rocks and are
  formed either underground from magma or above
  ground from lava.
• Most minerals are also igneous rocks.

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Igneous Rock Groups

• A) EXTRUSIVE IGNEOUS ROCKS forms when molten rock
  (lava) reaches the earth's surface and cools.
• Air and moisture cool the lava rapidly. The quick
  cooling doesn't allow the formation of large
  crystals so most extrusive rocks have small
  crystals or none at all. Also called FINE GRAIN
• 1) Basalt (most common fine grain)
• 2) Scoria (holes /trapping of air)
• 3) Pumice (holes /trapping of air)
• 4) Obsidian (no crystal)
• B) INTRUSIVE IGNEOUS ROCKS Sometimes the molten
  rock cools before it reaches the surface. Molten
  rock that is still underground is called magma.
  Because it forms deep beneath the earth's
  surface, it has more time to cool slowly and
  develops large crystals. Also called COARSE GRAIN
  
• 1) Granite (most common coarse grain)
• 2) Gabbro
• C) PORPHYRITIC an igneous rock whose cooling rate
  has changed and this gives it 2 or more different
  crystal sizes.

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Sedimentary Rocks

• For thousands, even millions of years, little
  pieces of our earth (Sediments) have been
  eroded--broken down and worn away by wind and
  water. (weathering erosion)
• These little bits of our earth are washed
  downstream where they settle to the bottom of the
  rivers, lakes, and oceans.
• Layer after layer of eroded earth is deposited on
  top of each.
• These layers are pressed down more and more
  through time, until the bottom layers slowly turn
  into rock. (compaction)
• Most common rock at earths surface. Fossils
  found in this type of rock.

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Sedimentary Rock Groups

• A) CLASTIC or DETRITAL classified by size of
  sediment (mud, sand, or gravel)
• 1)Gravel sized
• a) Conglomerate (round)
• b) Breccia (angular)
• 2) Sand sized
• a) sandstone
• 3) Mud sized
• a) shale
• b) siltstone
• B) ORGANIC classified by forming directly or
  indirectly from once living material.
• 1) Limestone
• 2)Chalk
• 3)Coal
• C) CHEMICAL formed by chemical means such as
  water evaporation and sediments cementing
  together.
• 1) rock salt
• 2) gypsum
• 3) limestone

Breccia, sandstone, shale
Organic (fossiliferous) limestone and coal
Rock salt and chemical limestone
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Metamorphic Rocks

• Metamorphic rocks are rocks that have changed
  ("morphed) into another kind of rock.
• These rocks were once igneous or sedimentary
  rocks.
• The rocks are usually buried deeply underground.
• The rocks are under tons and tons of pressure,
  which fosters heat build up, and this causes them
  to change. Sometimes chemical reactions change
  rocks also.
• 2 types of metamorphism
• Contact Metamorphism rocks heated by contact with
  magma or lava. Found around the edges of igneous
  rock formations.
• Regional metamorphism occurs over large areas of
  rock deep underground changed by heat and pressure

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Metamorphic Rock Groups

• 2 groups of metamorphic rocks.
• A) FOLIATED TEXTURE mineral crystals arranged in
  parallel layers. Due to different minerals having
  different densities they often separate into
  alternating light and dark bands.
• 1) Slate (used to be shale)
• 2) Schist (used to be granite, basalt or slate
• 3)Gneiss (used to be granite)
• B) UNFOLIATED TEXTURE no bands and do not break
  in layers.
• 1) Quartzite (used to be sandstone)
• 2) Marble (used to be limestone)

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The Rock Cycle

• The continuous changing of one rock type to
  another. (Sedimentary to igneous to metamorphic)
• It involves all processes between types.
  (volcanic activity, melting, erosion, deposition,
  compaction, burying, heat and pressure)

Rock Cycle Animation