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HOW ARE GEMSTONES FORMED
Most gemstones are mineral crystals that formed during
one of three rock making processes: igneous rocks, metamorphic rocks and
sedimentary rocks. Gemstones that have a mineral origin are found in rocks,
or in gem gravels derived from these rocks. Rocks themselves are made up of
one or more minerals, and may be divided into three main types. The
formation of these three types -igneous, sedimentary, or metamorphic - is a
continuous process, best described in terms of the rock cycle. Gem-quality
minerals within these rocks may be easily accessible at the Earth's
surface, or lie buried deep beneath it. Others, separated from their host
rock by erosion, are carried by rivers to lakes or the sea.
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IGNEOUS ROCKS
Deep within the earth's inferno is a stew of molten rock and gases, called
magma. As magma wells up within the earth, intense pressure builds forcing
the liquid rock toward the surface, sometimes breaking through to be known
as lava. It slowly cools forming igneous rocks, and within these rocks and
gas bubble spaces, interlocking crystals grow. The minerals present, the
cooling time and the environment will all play a role in the way these
crystals form. Examples of gemstones found in igneous rock: diamonds, topaz,
kunzite and spinel.
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METAMORPHIC ROCKS
Lastly, intense pressure and high temperatures can actually recrystallize,
transforming the composition of the rock. This can happen deep within the
earth's crust and it can also happen with direct contact with hot magma.
Emerald sometimes also forms in hydrothermals associated with magma. Other
examples of metamorphic gemstones include sapphire, jadeite and peridot.
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SEDIMENTARY ROCKS
Rock fragments near the earth's surface are often washed into riverbeds and
seabeds. Over time, layers of rock fragments, mud and other organic and
non-organic elements are compacted together in hard rock. Sometimes sea
creatures, bugs or other organic elements will get trapped within the rock
formations. Examples of sedimentary rocks include limestone, shale and
sandstone. In addition, most gemstones are found in sedimentary deposits.
Discovered in riverbeds, these alluvial deposits include metamorphic gems
such as sapphire and ruby.
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ORGANIC GEMS
Organic gems come from plants and animals. Natural pearls form around
foreign bodies that have made their way inside the shells of marine or
freshwater shellfish. Cultured pearls are produced artificially in large
fisheries, many in the shallow waters off the shores of Japan and China.
Shells treated as gems may come from animals as diverse as snails and
turtles, living in the ocean, in fresh water, or on land. Coral is made
up of the skeletons of tiny marine animals called coral polyps. Bone, or
ivory from the teeth or tusks of mammals, may come from
recently living animals or from fossils thousands of years old.
Amber is fossilized tree resin, collected from soft sediments or the
sea. Jet is fossilized wood, found in some sedimentary rocks. |
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Natural Gemstones |
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