Agate is a common translucent variety of quartz (silica) of various colors and waxy luster. Agate is the most common form of quartz and has been used as a gem and ornamental for a long time. Agate resembles flint, jasper, tiger's eye and petrified wood in both chemical composition and physical properties. Sometimes agate is found accompanied by opal. Agate is characterized by colorful, banded rocks primarily used as an inexpensive gemstone and in the production of grinding machines.
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Formation
Agates can occur in various kinds of rocks, although they are mainly associated with volcanic rocks and ancient lavas where they formed from silica within the molten mass spewed forth from volcanic eruptions, which was slowly deposited into nodules and cavities in the host rocks. Agates are composed of silicon dioxide. The siliceous matters are often deposited in regular layers forming a banded appearance similar to the rings of a tree trunk.
Occurrence
Agate is found all over the world. Important sources of agate are the United States, Brazil and Uruguay. In the United States, it is found in many western states like Washington, Montana, Idaho and Oregon. Arizona is famous for its petrified wood agate. Petrified Forest National Park is the source of petrified wood agate in the U.S. Petrified wood agate ranks third in commercially valuable gemstones worldwide.
Characteristics
Varieties of agates are characterized by brightness in color and peculiarity in shape. The outer layer of a raw agate is rough and sometimes pitted with cell-like cavities. Agates are chemically coagulated gel composed of alkali and silica. Many agates are empty inside. Agates are extremely weather resistant.
Types of Agate
A riband agate has straight bands. In eye agate, these bands appear as circular, in various colors. The moss agate contains matter of green, red, golden and black or other color combinations in the form of filaments or other shapes that resemble moss. In dendritic agate, manganese and iron oxides give rise to fern-like patterns suggestive of trees, bushes or landscapes.
Uses
Agates are used in the creation of ornaments like brooches, pins, marbles, paper knives, seals and inkstands. They are employed in the manufacture of grinding equipment to crush and mix chemicals because of their great rigidity and ability to resist acids. Agates are also used in the making of mortars and pestles.
Tags: wood agate, agate Petrified, petrified wood, United States, various colors, wood agate Petrified