2. Native Elements
Only a few minerals occur as pure
elements in the earth’s crust.
Gold Graphite Silver Sulfur Diamond Copper Platinum
Au C Ag S C Cu Pt
3. Most are found as chemical
compounds called minerals
Beryl
Be Al Silicate
Quartz SiO2 Calcite CaCO3
4. Rocks 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
6. ORES are rocks containing
valuable minerals
•
Hematite Malachite Galena
Iron Ore Copper Lead
Gold in
Quartz
7. 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
• Iron ores consist of haemetite,
magnetite, pyrite and limonite
• Diamond in W.A. is mined
from volcanic plugs called
Kimberlite pipes.
Crystalline
Haemetite is
used to make
jewellery
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
10. Physical Properties of
Minerals
• COLOUR
• HARDNESS
• CLEAVAGE
• SPECIFIC
GRAVITY
• STREAK
• CRYSTAL FACES
11. Colour......................
Most minerals are
coloured by a limited
number of metals
present as impurities.
The most common
elements affecting
colour are:
chromium, iron,
manganese, titanium
Minerals tend to
occur in a range
of colours, and
colour patterns
which help to
identify them
It is chromium which produces and copper.
the intense red of ruby and the
brilliant green of emerald.
12. 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
13. 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.
14. 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.
15. 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.
16. 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.
17. 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.
19. 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.
20. 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.
21. Refraction....................
• This is a measure of the mineral's ability to
bend a beam of light. This ability is called
refractive index.
Ruby coloured by chromium
Some
gemstones
can be
identified by
the spectral
colours they
produce.
Almandine garnet coloured by iron
-Measuring refraction using an optical instrument called a Refractometer.
22. 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.
