Title: Native Elements, Minerals Rocks
1Native Elements, Minerals Rocks Ores
2Native 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 -
3Most are found as chemical compounds called
minerals
- Beryl
- Be Al Silicate
- Quartz SiO2
Calcite CaCO3
4Rocks are mixtures of minerals and elements.
- Lapis lazuli
Unakite - Lazulite Boulder Opal
quartz,feldspar - Calcite opal in cracks epidote
- Pyrites of boulder
5- 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
6ORES are rocks containing valuable minerals
-
- Hematite Malachite Galena
- Iron Ore Copper Lead
Gold in Quartz
7ORES
- 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
8ORES
9- 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
10Physical Properties of Minerals
- COLOUR
- HARDNESS
- CLEAVAGE
- SPECIFIC GRAVITY
- STREAK
- CRYSTAL FACES
11Colour......................
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.
12Quartz 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
13Hardness................... -
- 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.
14Cleavage................
Distinct cleavage planes can be illustrated in
this box mica specimen
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- 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.
15Streak
- 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.
16Specific Gravity...................
- Â
- 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.
17Crystals
- 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.
18Next slides are advanced or extension only .
19Optical 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. Â
20Double 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.
21Refraction....................
- 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.
22What 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.