What is an Agate?

This agate nodule had an unusually shaped cavity that gave rise to this different agate. Richard Gross

What is an agate? Agate is a form of microcrystalline chalcedony quartz. It is the most popular type of chalcedony because of its banding, its brilliant colors, and numerous varieties. While banding is technically a requisite to be an agate it is common to refer to certain other forms of non-banded chalcedony as agate. Moss agate and eye agate are examples of non-banded chalcedony.

What is an Agate Facts

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Agate has a seven Mohs hardness, making it desirable in the lapidary trade. Agate is translucent and exhibits a vitreous luster. As with other varieties of quartz, its chemical formula is SiO2. The name agate comes from the river Achates in Sicily and was given that name by the Greek philosopher, Theophrastus. Agate names can be derived from the location where they are found such as Botswana agate or Laguna agate or because of a feature they exhibit like lace, fire or moss.

How Agates Are Formed

Agate formation takes place when silica solutions fill voids in cavities layer by layer such as in Florida’s agatized coral. The voids typically are in solidified volcanic lava flows and the layering over long periods of time can result in different colors because of chemical changes in the silica solutions. The layering can deposit the chalcedony in concentric circles around the wall of the cavity or build the layers up from the bottom of the cavity.

This Baker Ranch agate was collected south of Deming, New Mexico. The contrasting colors make this agate collectible.
Richard Gross

Decorative Agates

Agate is used to produce cabochons, beads, and free-form objects in jewelry making. Book-ends, ashtrays, and sculptures are also made using agate.

Positively Agate

In the metaphysical realm, many wonder what is an agate and how can it help me. Agates are said to change negative energy into positive energy and to heal anxiety and internal anger. Agate may also help with concentration and boost mental function.

Laguna agate is found near the tiny village of Ojo Laguna in Chihuahua state, Mexico. It is a lapidary favorite because of its brilliant colors and exceptional banding.
Richard Gross

Where to Find Agates

In the United States, agates are found in Oregon, Wyoming, Montana, Arizona, Idaho, California, Washington, New Mexico, Iowa, Wisconsin, Michigan, Minnesota, Utah, Florida, Colorado, Arkansas, and Nevada. Around the world, they are found in Australia, Germany, Brazil, Czechia, Botswana, Mexico, Morocco, Afghanistan, Argentina, Canada, Chile, India, China, and over 40 other countries.

This field guide about what is an agate appeared in Rock & Gem magazine. Click here to subscribe. Story by Richard Gross.


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