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Gemstones Facts


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Agate agate gemstone

Mohs scale hardness: 7

Agate is a hardstone with curved, bands of different colors or other markings used in jewelry, it is a type of chalcedony, a microcrystalline variety of quartz. You can find agates in all colors of the rainbow, although blue and green are quite rare. Like the rest of chalcedony members, its chemical formula is SiO2 and the colours of the stone come from impurities in the silicon dioxide. Agate is the most common variety of chalcedony and the most creatively striped gemstone by nature.

In order for the stone to be called as an agate, it has to show the band effect. Without it, people will only recognize the stone as any other variety of chalcedony. The banded appearance is due to the other substances deposited in the layers of the stone. These bands may consist of other quartz such as amethyst and rock crystal or chalcedony such as onyx, carnelian or even jasper. Agates are identical in chemical structure to flint, jasper, chert, tiger eye and petrified wood, and are often found in association with opal. Since the stones are porous, sometimes agate stones are dyed to enhance its colour and beauty. Most of the agate that people used for ornamental purposes is artificially colored.

How Agates are Formed

Natural agates develop when an empty bubble, pocket or space inside a host rock filled with silica-rich water and other mineral impurities and eventually coagulating into a gel. The gel dissolves surrounding metals such as iron and leaves a layer of residue which settles into this gel. The layer is then followed by another layers, until over time this acidic type of gel loses water and the entire subtance begins to crystallize. Eventually, the crystallized gel and entire pocket of dissolved layers hardens. If at some point water breaks open all of these bubbles and washes into them, the material of agate will be broken apart and drawn into lakes, rivers and oceans. Although they can form in any types of host rock, most of agates developed in ancient volcanic lava.

Drusy (sometimes misspelled as druzy), the tiny quartz crystals often form within the stone and add to the uniqueness and beauty of individual stones. Lapidaries often cut just the drusy from the stone and these drusy cabochons are used by the jewelers as the main stone.

If agate is heated or left in sunlight, its color will fade and the stone can crack. Keep it in a dark and cool place is safe enough. To clean the gemstone you can wash it in soap and mild detergent, avoid using abrasive or harsh chemicals on it. Although the stone is very hard, it can crack or scratch if it is handled roughly.

Different Types of Agate

The name of the stone, agate was given by a Greek naturalist and philosopher, Theophrastus who discovered it between 4th and 3rd centuries BC in the river Achates in Sicily. Raw agates can be found in Uruguay, Brazil and United States. Many products made from agate from all parts of the world comes from Germany (the agate’s capital processing). Common types of agate are moss agate, blue lace agate, petrified wood and tree agate.

Moss agate: Dark green in color with clear patches and contains visible impurities. This is the most-sought-after variety and it is also known as Mocha stone. Do note that many non-banded forms of chalcedony such as moss agates are often erroneously called ‘agates’. True agates are concentrically banded. Included and mottled chalcedonies are more properly called simply ‘chalcedony’.

Dendritic agate: A colorless or whitish-gray in color with fern- or tree-like markings known as dendrites. The variety name ‘agate’ is given to this stone even though the gem does not exhibit the banding typical of agate.

Riband agate: In this variety, the bands appear as straight lines across the gemstone. These stones are also called as ribbon agate. Such agate, witth white bands alternating with bands of red, brown or black is called onyx.

Ring agate: Agate with concentric ring pattern, looking like an eye. It is also called as eye agate.

Plume agate: Agate with dark-colored, plume-like structures within the material. Color varies from shades of white, blue, red and yellow. Unites States is the primary source for this variety. The inclusions of this stone sometimes resembles feathers, flowers or plants.

Fire agate: A variety of agate containing inclusions of limonite or goethite, producing an iridescent effect or "fire."

Agates are the anniversary gemstones for those who celebrate their 12th year of marriage and considered the mystical birthstones for the month of September.

It is believed agates have special properties:

Astrologically, agates are associated with the zodiac signs of Gemini.



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