GEMSTONES

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GEMSTONES By Audree,Jordan,Josh, and Alex
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A gemstone or gem (also called a precious or
semi-precious stone) is a piece of attractive
mineral, which when cut and polished is used to
make jewelry or other decorations.
Precious Has beauty, durability, size, and
rarity.(Diamond, emerald, opal,ruby,safphire) Sem
i-precious only two of those (quartz, Jade)
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The Mohs Scale characterizes the scratch
resistance of different types of minerals through
the ability of a harder material to scratch a
softer material. It was created in 1812 by the
German mineralogist Friedrich Mohs.
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Most gemstones are hard, but some soft minerals
are used in jewelry because of their luster or
other physical properties that have
value. Luster the way light interacts with the
surface of a crystal, rock, or mineral.Sheen.
Greasy Luster Greasy minerals resemble fat or
grease. A greasy lustre often occurs in minerals
containing a lot of microscopic inclusions. Some
examples are opal and cordierite.Many minerals
with a greasy lustre also feel greasy or smooth.
Adamantine Luster Adamantine minerals have the
best lustre. It is mostly seen in diamond.Diamond
minerals are transparent and refract the light
the best.Minerals with a true adamantine lustre
are uncommon.
Dull Luster Dull (or earthy) minerals have little
to no lustre, because they are coarse and grainy,
which scatters light in all directions instead of
reflecting it. These minerals are not used for
jewlery or decorations.
Metallic Luster Metallic minerals have the lustre
of polished metal.
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Pearly Luster Pearly minerals consist of thin
transparent sheets. Light reflecting from these
layers give them a lustre similar to Pearls.
Submetalic Luster Submetallic minerals have
similar lustre to metal, but are duller and less
reflective
Resinous Luster Resinous minerals have the
appearance of chewing gum chewing or plastic
Waxy luster
Vitreous Luster Vitreous minerals have the lustre
of glass. This type of lustre is one of the most
commonly seen, and occurs in transparent or
translucent minerals
Silky Luster Silky minerals have a parallel
arrangement of fine fibers. This makes the
minerals look like silk.
minerals have a luster resembling wax.
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Magmatic Crystallization Cooling Magma produces
crystals of different kinds of minerals. Crystals
are formed from the lava when the volcano erupts.
Examples moonstone, topaz and corundum.
Metamorphic deposits When a rock is in a high
temperature and or high pressure, the chemical
components get rearranged into new minerals. Gem
minerals formed are diopside, corundum,
andalusite, sillimanite, kyanite, epidote, and
garnet.
Pegmatite Towards the final stage of magmatic
crystallisation, a thin silicate liquid remains
and if this is squeezed into surrounding rocks,
it produces pegmatites containing very large
crystals. ExamplesTourmaline, topaz, beryl,
quartz and spodumene are some of the common
pegmatitic gem stones.
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Metamorphic deposits When a rock is in a high
temperature and or high pressure, the chemical
components get rearranged into new minerals. Gem
minerals formed are diopside, corundum,
andalusite, sillimanite, kyanite, epidote, and
garnet.
Placer or Alluvial deposits Some minerals are
highly resistant to weathering and when the rest
of the rock has decomposed and disintegrated they
are carried by flowing water.Because of gravity,
they get deposited on the river bed making a
gem.Examplesdiamond, ruby, sapphire,
chrysoberyl, zircon, garnet,and quartz
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topaz, beryl, quartz
moonstone, topaz and corundum
diamond, ruby, sapphire
kyanite, epidote, and garnet
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