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Natural Agate

A subvariety of chalcedony, agate is a kind of crypto-crystalline quartz. It is frequently banded with successive layers varying in color and translucency. The banding is thought to be a result of a rhythmic deposition of silica. In other cases, the agate is formed by a complex process in which silica permeates and replaces the buried remains of a living organism. This process known as petrification or fossilization, occurs so slowly that the original form remains. Molecules of the organic material are removed and replaced bit by bit by inorganic material (silica in solution). In the most optimal of cases, delicate and minute details of the original cellular structure have been reproduced. Bones, teeth, shells, and wood are often preserved in this manner. The resulting material is descriptively known as silicified or agatized. Some well known kinds of agate include onyx, sardonyx, dendtritic agate, moss agate, agatized coral, petrified wood, and dinosaur bone. Agate is hard and tough enough to be incorporated into jewelry and other ornamental items.

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Agate Profile

Color information: Blue, yellow, green, yellow, orange, brown, gray.
Refractive Index: 1.530 - 1.539
Chemical Composition: SiO2
Hardness: 6.5 - 7
Density: 2.57 - 2.64
Crystal Group: Hexagonal
Ocurrence: Scotland, U.S.A., India, England, Italy, Brazil, Uruguay, Germany, Egypt, Indonesia, and many other localities.
Sign of the Zodiac: N/A
Month of the year: N/A
Agate Agate Agate Agate
Some kinds of agate may be dyed or heated to improve or change colors or to heighten translucence. Immersion in a hot sugar solution followed by immersion in hot sulphuric acid and heating can produce black. A blue color once known as Swiss lapis is produced by immersion in potassium ferrocyanide and subsequent warming in a solution of ferrous sulphate. Chromium alum and potassium dichromate and nickel compounds may be used to produce a bright apple green. Impregnation with iron and heating may give reddish brown and red colors and yellow to greenish yellow may be obtained by heating dry agate that has been treated with concentrated hydrochloric acid.

Moss Agate/ Dendtritic Agate

Moss Agate is a pale bluish grey or yellow translucent to subtransparent chalcedony containing dendritic (plant like) inclusions of various oxides. The colors vary and most are black but green and red dendrites are also common.


Onyx is the name used for agate with milky–white or white bands alternating with bands of black or dark brown. White with brown bands may also be known as sardonyx.

Agatized Coral

Coral is the outside skeleton of tiny ocean animals called polyps which live in colonies attached to hard underwater surfaces. When alive, polyps combine their own carbon dioxide with the lime in warm seawater to form a limestone-like hard surface, or coral. Agatized coral occurs when silica in the ocean water hardens, replacing the limy corals with a form of quartz. This long fossilization process (20-30 million years) results in the formation of a "pseudomorph" meaning that one mineral has replaced another without having lost its original form.

Petrified Palm Wood

The name petrified palm wood refers to a group of fossil woods that contain prominent rod-like structures within the regular grain of the silicified wood. Depending upon the angle at which they are cut by fracture, these rod-like structures show up as spots, tapering rods, or continuous lines. The rod-like structures are bundles that comprise part of the woody tissues that gave the wood its vertical strength. The material is a favorite of rock collectors because it exhibits these well-defined rod-like structures in a variety of colors.

Dinosaur Bone

What we today call dinosaur bone is more correctly and descriptively known as silicified fossil of dinosaur bone. Fossils are the remains of prehistoric animals or plants. Although fossilized dinosaur bones are found in many places around the world, from Argentina to Mongolia to Madagascar, the highly silicified and beautifully colored dinosaur sometimes called gem bone, is almost exclusively found in a relatively small area in the United States, the Colorado Plateau. Most of the areas that produce quality bone are in Colorado and Utah. When the dinosaurs lived there it was an area that included both land and water, with swamps, lakes, and shallow oceans bordered by continental shelf, rising into ancient mountains. As geologic time passed the climate changed, becoming more arid. Volcanic activity increased, and with it volcanic sediments, rich in silica were carried by the rivers and deposited as the seas retreated. This proved to be an ideal environment for the burial and subsequent preservation of the remains of many a dinosaur.

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