What is an Agate?

Mary McMahon
Mary McMahon

Agate is a type of chalcedony, a milky form of quartz, that appears in a striking banded formation that people have found aesthetically pleasing for centuries. Chemically, it is identical to quartz, amethyst, and carnelians, but because it forms in a different way, this stone looks radically different. Like all forms of chalcedony, its chemical formula is SiO2, and the colors come from impurities in the silicon dioxide. In addition to coming in a range of stunning colors in nature, the highly porous stone is also sometimes dyed to be more vivid in color.

Brazil is a source of raw agate.
Brazil is a source of raw agate.

Brazil, Uruguay, and the Western United States are all sources for raw agate. Traditionally, Germany has been the capital of agate processing, and products are shipped from Germany to jewelers and stores all over the world. The distinctive stone is used in jewelry and to make decorative household ornaments such as bookends and coasters. Some religious ornaments are also made from it, including worry beads and meditation stones carried in many cultures.

Germany is the capital of agate processing.
Germany is the capital of agate processing.

Deposits of volcanic rock frequently harbor agate, which is formed when silicates make deposits in cracks and holes in rock. The outer layer of the stone tends to turn dark and crusty, but the layers inside form rich bands of color that can be cut in cross section and polished for use in jewelry. It is very similar to onyx, another form of chalcedony that forms in successive layers, but agates tend to have more irregular bands and a wider range of colors.

Some agates are so distinctive that they carry their own names, such as moss agate, a unique form that has feathers of rich mossy green riddling a white stone. Iris agate, another special occurrence of the rock, has a remarkable iridescent sheen. Both forms, along with other varieties, are used in rings, bracelets, and necklaces, and are usually cut large to show off the rich bands of color. Often, a piece of jewelry made with the stone will have an unusual shape to accommodate a unique and striking pattern.

If kept in heat and sunlight, agate can crack and fade, so owners should make sure to store it in a cool, dark place. If the stone becomes dirty, it can be washed in soap and a mild detergent solution, but people should do not use harsh or abrasive chemicals on it. Agates can scratch or crack if they are handled roughly, so owners should be gentle with jewelry made from it, and try to avoid slamming it into things or dragging it across hard surfaces.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


Does anyone know how hard agate is on the Moh scale?


@indigomoth - I've seen it done to really good effect though particularly with agate beads. And I think a lot of the time the dyes are enhancing the original colors and you don't realize that they're even there.

I quite like the rainbow agate necklaces you can get and those are usually helped by dyed stone. Although my favorite kind of agate bead is what they call a spider web agate bead. Each one is so unique and I love the subtle colors of them.

If you want to get some agate beads I would recommend buying them from wholesalers online as that's the cheapest method that I've found. Do shop around, at any rate, as you'll find that prices vary a lot.


I really don't like it when agate stones are obviously dyed. You can get those stones which have been made into a really bright pink or green or purple and it looks completely unnatural. I guess this is because agate is already fairly noticeable and bright, even when it hasn't been dyed.

I've seen it especially in the flat chunks of stone that people buy for display (they look like a section of a tree with all the rings) but sometimes you see it in beads and things as well. There's already such a wide range of agate colors and types, it just seems ridiculous to ruin the beautiful original colors of the stone.

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