Natural Gem Stones

By Author: Mohan Chen
Total Articles: 434
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Deep within the earth, molten rock and gasses continually move against the earth's crust. It is within this extremely high pressure and heat that diamonds and peridot are formed. Diamonds begin to crystallize in the magma 109 to 149 miles beneath the earth's surface, and peridots are formed 20 to 55 miles below. As the earth's crust continually moves, these deposits begin to work their way toward the surface.
Generally, Natural Gem stones are classified through four processes, although some gemstones undergo more than one process in their formation.
1. Molten rock, fluids, and gasses
2. Environmental changes
3. Surface water
4. Formation in the earth's mantle
Magma Crystallization
Minerals are formed as the molten rock, or magma, cools on its journey to the earth's crust. Different elements in the magma create different minerals, and these minerals can crystallize as they head toward the earth's crust, forming rubies, sapphires, moonstone, garnets, and zircons embedded within fine-grained rocks.
Gas Crystallization
Some gemstones ...
... form within gas bubbles which occur when magma decreases in pressure quickly, as in a volcanic eruption. A high concentration of various elements in the bubbles creates garnets, topaz and spinels.
Hydrothermal Action
Sometimes water enters the mantle through cracks in the crust and combines with special elements like carbon dioxide, fluorine, beryllium, and other elements that are easily vaporized. This hydrothermal liquid may dissolve minerals or combine with surface water in cracks to form mineral veins. With time, temperature, pressure, and available space, crystals such as amethysts, topaz, and emeralds are formed.
Pegmatite
A pegmatite is a cavity formed by volatiles, or quickly vaporized elements. Within the pegmatite elements crystallize forming topaz, tourmalines, kunzites, aquamarines and morganites.
GEMSTONES CREATED BY ENVIRONMENT CHANGES
When magma forces itself through existing rock in the earth's crust, as in a volcano, the heat can re-melt the already formed rock and create new crystals that are more heat-resistant than before. Lapis lazuli, garnets, diopsides, and spinels are the result.
When continental plates shift on the earth, the resulting heat and pressure form mountains. The existing mineral crystals become unstable and change into new crystals, creating tanzanites and varieties of garnets.
SURFACE WATER
Rain and water from streams, lakes, and oceans can make new gems as it passes over and combines with different chemicals. As water levels change, some of these new stones are deposited on the surface ground, or upper levels of crust. Turquoise, opals, malachite, amethyst, azurites, and agates are often left exposed.
FORMED IN THE MANTLE
The earth's mantle is 83% of the earth's volume and 1,864 miles thick. Where the mantle and crust meet, there is constant motion, pressure, and extreme temperatures. It is this combination of conditions that create the hardest compound known to man, diamonds.

Natural Gem stones, when mined, are not always as colorful as they appear in a jeweler's case or shop. In order to bring about the intensity of a gemstone's color, enhancements need to be made. These can include heating, oiling, dyeing and irradiation.

Heating
Heat treatment is the most common form of gemstone enhancement. Techniques can vary, from putting stones into a fire and "cooking" them, to using gas or electric furnaces at certain pressures to receive the desired effect. Heating is a permanent technique, used to enhance, intensify or a change a gemstone's color. Examples of heat-treated gemstones include carnelian, aquamarine, sapphire, citrine, ruby, amethyst and tourmaline.
Irradiation
Irradiation of gemstones to change or increase their color can occur naturally within the earth, but may take millions of years. Artificial irradiation only takes a few hours. Irradiation uses gamma rays, neutrons or high energy electrons to change a gemstone's color. This process is often followed by a heat treatment. Topaz, which in it's natural form, is a very pale blue to clear color, is irradiated to bring about its deeper shades of blue and even green. Other examples include tourmaline, ruby, chrysoberyl, cat's eye, kunzite and even cultured pearls.
Oiling
Emeralds are commonly "oiled" whereby oil, resin or wax is used to fill fissures in the gemstone's surface, thus making the stone's color more uniform. Other gemstones that may be oiled are opals (though rarely) and peridot.
Dyeing
Intensifying a gemstone's present color or improving its uniformity is sometimes brought about by dyeing, where color is added to the gemstone. Black onyx is always dyed to keep its rich, black color. Other gemstones that may be dyed are rose quartz, amber, carnelian, agate, lapis lazuli, jade, serpentine and turquoise.
Chemical Diffusion
The use of high heat temperatures with chemical additives to a stone's surface is chemical diffusion. The process leads to a more intense color or a complete color change altogether. Because chemical diffusion often results in artificially altering a gemstone's color, it must be disclosed on documents and advertising of the gemstone on which it is used. Rubies, sapphires and green topaz are sometimes chemically diffused.