The Six Types Of Agate

 Agate is a type of chalcedony with a waxy luster that varies from semi-translucent to opaque. With its wide variety of colors and patterns, it's one of the most popular semi-precious stones out there. Somewhat like flint, agate can be found in various parts of the world, but that doesn't mean it's structurally the same. Agate is one of the most common types of rock. Everyone knows the colorful variety, often used as beads or decorative jewelry. Agate has been mined since prehistory when it was first noticed by humans. 

Fire Agate with amazing Sagenite Spray 

Formation of Agate

Agates form when silica-rich fluids fill voids (crevices, cavities, fossils) in volcanic rock and other types of rocks. As the fluid cools, it forms banded chalcedony that fills the voids and often creates concentric banding patterns around the original cavity or fossil. The color of the bands depends on trace elements in the surrounding rocks. For example, iron can create red bands in an agate while manganese can create pink bands.

Agate (Borden Formation, Lower Mississippian; eastern Kentucky, USA)

Agate Types 

 There are six main types of agate: banded, moss, dendritic, fortification, sagenite, and agatized wood. Each has its own set of characteristics. Let's take a look at each below. I will break down the different agate types and include pictures for easy identification. Each type forms in a different way and is easily recognizable, along with having its own unique set of physical characteristics.

Banded Agate

Banded agates are among the most common forms of this gemstone. They have layers that alternate in color or hue. Sometimes the layers look like stripes or bands, while other times they resemble clouds. They’re characterized by their smooth and spherical shape, where bands of color appear to float within a layer of translucent chalcedony. The colors of banded agate depend on the minerals found in the layers, which can vary widely. Some of the most popular colors are red, blue, green, and brown. If a stone only has two colors, it’s called an eye agate.

Banded Agate-Fairburn Agate -ultimately derived from the Minnelusa Formation, Pennsylvanian-Permian

Moss Agate

Moss agates have a translucent appearance. They typically have green markings, but can also come in gray or brown, which resembles moss and lichens growing on rocks and trees. Moss agates may have dendrites that look like ferns or leaves. Moss agate is a variety of chalcedony that has moss-like inclusions formed from other minerals such as iron or manganese. The stones usually have a black or white background with green mossy inclusions, but other shades are possible depending on the minerals that form them.

Moosachat-Moss Agate

Dendritic Agate

Dendrites are fern-like or tree-like inclusions in some types of gemstones. The dendrites found in dendritic agate are usually made of manganese or iron oxides, but they can also be made of copper or chlorite. The dendrite inclusion must cover at least 50 percent of the stone to be considered dendritic agate; otherwise, it’s just an ordinary chalcedony with dendrites, not an exquisite dendritic agate! Dendritic agates look like green mosses or trees and are known as tree agates or landscape stones. They also have black or brown dendrites that resemble tree branches. Landscape stones are often used in decorative arts and jewelry pieces.

Dendritic Agate

Fortification Agate

Fortification Agates get their name because they look like a castle wall or fortifications within a city wall. These stones feature concentric circles that form a bullseye pattern. Fortification agates were named for their resemblance to castle fortifications. The stones have one or more layers of larger crystals (usually quartz) within smaller crystals, which gives them a layered appearance like stone walls with rows of windows or crenelations (the gaps between battlements). 

Indistinctly banded fortification agate | Captain Tenneal

Sagenite Agates

Sagenite Agates. Sagenite is a variegated variety of agate with needle-like crystals inside it that look like a mass of hair or fibers embedded in the stone. Sagenite Agate - Sagenite agate has fern-like patterns. The patterns are formed when tiny radiating crystals grow inside the stone. These crystals are sometimes called "angel's hair."Sagenite comes from the Latin word sagena, which means "sailor's rope." It was given this name because the fern-like patterns resembled ropes that were used on ships. Sagenite agate occurs in several places around the world, including California and Arizona in the United States, Namibia in Africa, and Brazil.

Fire Agate with amazing Sagenite Spray 

Agatized Wood

agatized wood: It's formed when petrified wood is replaced by agate while maintaining its original structure. A piece of agatized wood will look like a cross-section of a tree trunk with rings and all! Some types of agate are given a special name due to their location rather than the way they form. When you see names like Mexican Lace Agate or Botswana Agate, those are referring to where the stone was found rather than how it was formed.

Agatized Wood


These are just six of the more popular types of agate that you're likely to run into as a collector. Of course, there are also moonstone varieties and fire opal agate, among other types. The best way to learn about all types of agate is to speak with someone who knows what they're talking about, such as an experienced gem-cutter or gemologist. After experimentation, by observing different agates you may even come up with your classification system. I hope you found this article helpful. See how your favorite flavors of agate stack up, and if you're aching to get your hands on one of these beauties, you might have some new ideas to try out.

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