Native Elements, Minerals Rocks & Ores

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Native Elements, Minerals Rocks Ores

• Year 9
• Geology Topic

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Native Elements Only a few minerals occur as
pure elements in the earths crust.

• Gold Graphite Silver Sulfur
  Diamond Copper Platinum
• Au C Ag S
  C Cu Pt

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Most are found as chemical compounds called
minerals

• Beryl
• Be Al Silicate
• Quartz SiO2
  Calcite CaCO3

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Rocks are mixtures of minerals and elements.

• Lapis lazuli
  Unakite
• Lazulite Boulder Opal
  quartz,feldspar
• Calcite opal in cracks epidote
• Pyrites of boulder

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• CHEMISTRY
• An element contains only one type of atom
• A compound contains two or more elements
  chemically combined
• A mixture contains elements and or compounds that
  are not chemically combined

• GEOLOGY
• A Native Element contains only one type of atom
  and is found naturally on earth in its pure form.
• A mineral contains two or more elements
  chemically combined
• A rock contains a mixture of elements and
  compounds

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ORES are rocks containing valuable minerals

• Hematite Malachite Galena
• Iron Ore Copper Lead

Gold in Quartz
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ORES

• Gold in W.A. is mined from tellurides, chlorites,
  quartz veins and in copper ores at Telfer
• Gold nuggets are native elements.

• Copper is found in cuprite, malachite and azurite
• Native copper is rare

• Diamond in W.A. is mined from volcanic plugs
  called Kimberlite pipes.

• Iron ores consist of haemetite, magnetite, pyrite
  and limonite

Crystalline Haemetite is used to make jewellery
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ORES
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• Only a few minerals are rock forming and most
  rock is made from a combination of the commonest
  of these such as feldspars, quartz, mica,
  olivine, calcite, pyroxene and amphiboles

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Physical Properties of Minerals

• COLOUR
• HARDNESS
• CLEAVAGE
• SPECIFIC GRAVITY
• STREAK
• CRYSTAL FACES

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Colour......................
Minerals tend to occur in a range of colours, and
colour patterns which help to identify them

• Most minerals are coloured by a limited number of
  metals present as impurities.
• The most common elements affecting colour are
• chromium, iron, manganese, titanium and
  copper.

•      

It is chromium which produces the intense red of
ruby and the brilliant green of emerald.
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Quartz displays a profusion of colours, patterns
and optical effects unsurpassed by any other gem

• colourless is rock
  crystal
• purple quartz is amethyst
• yellow is citrine
• brown is smoky
  quartz
• pink is rose quartz.
• black is
  morion

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Hardness................... -

• Hardness depends upon the forces holding the
  atoms of the mineral together.
• In 1812, a scientist, F. Moh devised a scale of
  hardness into which all minerals can be placed.
• He selected ten minerals and arranged them in
  order so that any one mineral could be used to
  scratch only minerals which are less.
• Diamond is the- hardest natural material, 140
  times harder than corundum.

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Cleavage................
Distinct cleavage planes can be illustrated in
this box mica specimen

• The manner in which a mineral splits is an aid to
  identification.
• These planes are related to the lattice work of
  the mineral's atomic structure.

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Streak

• When minerals are scratched, the powder that is
  made by the scratch is called the streak.
• Sometimes the colour of the streak can be used to
  identify the mineral.
• Eg. Haemetite a black mineral has a red streak.
  No other black mineral has a red streak.

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Specific Gravity...................

•  
• It was Archimedes who first worked out the
  principal of specific gravity or relative
  density. Specific gravity is defined as the ratio
  of the weight of a substance compared to that of
  an equal volume of water.
• For example, a piece of galena (lead ore), with a
  specific gravity of 7.4 will feel much heavier
  than a piece of quartz of a similar size but with
  specific gravity of 2.65, reflecting the way the
  atoms are packed together.

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Crystals

• Crystals are minerals or elements that have
  been cooled slowly enough for crystals to have
  formed.
• Such conditions occur most often in pegmatites
  or pipes.
• Crystals can be classified by their shapes
  into seven groups.

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Next slides are advanced or extension only .
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Optical effects.

• In diamond the 'fire' and sparkle is caused
  by dispersion as the gemstone acts like a prism.

• The brilliant colours displayed by opal are
  caused by the light being scattered as it passes
  through planes of regularly spaced voids between
  the transparent silica spheres.  

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Double Refraction .

• Double refraction can be seen in a piece of
  Calcite.
• Light separates into two rays which makes images
  seen through the crystal appear to be doubled.

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Refraction....................

• This is a measure of the mineral's ability to
  bend a beam of light. This ability is called
  refractive index.

Some gemstones can be identified by the spectral
colours they produce.
Ruby coloured by chromium
Almandine garnet coloured by iron
-Measuring refraction using an optical instrument
called a Refractometer.
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What makes a mineral a Gemstone?

• There are over two hundred recognised gemstones.
  Most are minerals and are cut from naturally
  occurring crystals.
• To qualify as a gem, the specimen should be hard
  and tough to resist scratching and have beautiful
  clarity, colour or 'fire'. Value is based on
  rarity and rare quality.