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Origin
of Gems
Earth is a gigantic chemical factory, within which all
the chemical elements are mixed and combined. Minerals
are naturally occurring chemical compounds and elements.
Every mineral is characterized by a definite crystal
structure and a chemical composition that varies within
defined limits.
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A
rock is made up of one or more minerals. Rocks are classified
according to the minerals they contain and the process
of their information. Igneous rocks form when molten
material cools and so¬lidifies, either at depth
or at or near the earth's surface. |
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Sedimentary rocks form at the earth's surface.
They consist of the remains of marine organisms that settled
and deposited in an ocean or lake, or the com¬pacted and
solidified debris of rocks exposed to the erosional forces
of wind, water, and ice. Such erosional fragments are called
sediments.
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DIAMONDS,
GEMSTONES & CRYSTALS
FACTS & FIGURES |
| Metamorphic
rocks are formed when enormous compressional forces,
sometimes accompanied by heat, crush, deform,
and alter pre-existing rocks of various kinds.
Such forces are due to movement in the earth's
crust, and the rock alteration process is called
metamorphism.
Specific types of minerals and gems are associated
with specific rock types. A knowledge of rocks
is essential in prospecting for minerals. Quartz,
for example, is extremely common. It even makes
up most beach sands! But gem quartz occurs only
in limited geologic environ¬ments.
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The
gem-mining areas of the world are limited in number.
The most important sources of the world's colored
gemstones are in sedimentary deposits, such as
gravel beds. Next in importance is the pegmatite
dike, a special type of igneous body in which
large crystals may form. |
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Some
gems also form in metamorphic rocks, especially marbles. Accurate
production statistics are available on diamonds, but not for
colored stones. Most gem mines are small compared to diamond
mines, and some are worked only when demand creates high enough
prices for the gems they yield. These factors prevent a "flood"
of colored gems from entering world markets at one time. |
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