Agate, Meaning, Properties, and Facts

What is agate

Agate is chalcedony laid down in bands that follow the walls of the hole it filled. Each band differs a little in color, translucency and grain, so a cut slice shows rings like a contour map. Agate stone, agate crystal and agate rock all name the same thing in shops, though its crystals are microscopic fibers of quartz rather than visible points. The Smithsonian's agate specimen page shows a museum example.

Agate properties

Agate properties are those of chalcedony: hard, tough, slightly porous and stable, which is why people have carved it into beads, seals and tools for thousands of years (mineral data on Mindat's chalcedony page):

Where agate is found

Agate is found worldwide, mostly in volcanic rock where gas bubbles left holes, and also in some sedimentary rocks. The biggest commercial source is Rio Grande do Sul in southern Brazil, with neighboring Uruguay, which supply most slices, geodes and bookends. Other classic sources include Botswana, known for fine pink and gray banding; Chihuahua, Mexico, home of Laguna and crazy lace agate; and the Lake Superior region, where iron-red agates wash out of glacial gravel and Minnesota made Lake Superior agate its state gemstone. Colorado has agate in its volcanic country too, and the Colorado crystals and collecting hub covers where people dig.

Types of agate

Types of agate are named for their pattern, their locality or both. Fortification agate has angular bands like the walls of a fort; Lake Superior, Botswana and Laguna agates are named for where they come from; crazy lace twists in tight, busy bands; and moss agate has green or black fern-like inclusions instead of bands, so purists call it chalcedony, not true agate. Fire agate is chalcedony with iridescent layers of iron oxide, and onyx is chalcedony with straight, parallel bands.

How agate forms

How agate forms is still debated in its details, but the outline is clear. Silica-rich water seeps into a cavity, often an old gas bubble in lava, and deposits chalcedony on the walls in thin layers, with changes in the water's chemistry making bands of different colors. If the cavity never fills, the open center can grow quartz or amethyst crystals, making an agate geode, as how geodes form explains.

How to tell if agate is real

How to tell if agate is real usually means telling natural color from dye. Natural agate comes in earth tones: white, gray, soft blue, tan, orange, red and brown. Electric blue, hot pink, purple and bright green slices are almost always dyed, a centuries-old practice, with the dye soaking deepest into the most porous bands and pooling in cracks. Dyed agate is still agate. Glass imitations show bubbles and swirls, and plastic feels warm and light, while real agate feels cool and can scratch glass.

Agate care: water and sun

Agate care is easy because agate is water safe and hard. Agate can go in water for a rinse with mild soap, and natural colors hold up in the sun, but dyed agate can fade in strong light and bleed color in long soaks, so keep dyed slices out of sunny windows. Dry it with a soft cloth.

Agate meaning

Agate meaning, in crystal lore, is balance and steadiness, with each color given its own job. That is belief, not chemistry, and agate benefits sit in the same box. The history is solid: the Greek writer Theophrastus named the stone after the Achates River in Sicily, and Greeks and Romans carved agate into seals, rings and cameos.

Agate for sale

Agate for sale on geoslut arrives in drops: each piece is one of one, photographed in daylight and labeled with its locality, and the list hears about every drop first. Agate price depends on natural color, banding, size and locality, and dyed slices cost far less than fine natural agates.

Agate FAQ

What does agate look like on the outside?

Agate looks like a plain, lumpy rock on the outside, often a pitted, waxy or chalky nodule, and the bands only show where it is broken or cut. Hold a thin edge to a light: agate glows because it is translucent.

Is agate water safe?

Agate is water safe: it is hard chalcedony that does not dissolve or soften, though dyed agate can bleed color in long soaks.

Is agate a crystal?

Agate is made of crystals, but they are microscopic quartz fibers, so it never forms the visible points people usually mean by a crystal.

What is the difference between agate and chalcedony?

The difference between agate and chalcedony is banding: agate is chalcedony with bands, while plain chalcedony has one even color.

Sources

• Agate, Wikipedia
• Chalcedony, Mindat
• How geodes and agates form, Kentucky Geological Survey