Agates are a subject of their own, with various varieties creating an amazing display. While all share some of the same characteristics, each also provides their own impressive visuals. The trick is in knowing what actually makes up each type of agate.
So let’s dive in and talk about the different types of agate!
A Word About “Agate”
Agate is a strange word, used in a wide variety of ways. In the past, even the recent past, it primarily referred to various types of banded chalcedony. These types of agate (generally fortification or seam agate) have strong banding patterns.
In recent days, agate is mostly a reference to any kind of transparent, including chalcedony. The inclusions can form in different ways, ranging from complex 3D shapes to simple coloration, which is what makes the family so varied.
I’ll be using agate in the modern sense for this article.
This article is about specific types of agate without regard to their locality. The locality of a stone is often included in the name and small differences in appearance.
We’ll ignore trade names for the time being so that we can focus on the good stuff: the actual differences between types of agate.
So, let’s check them out!
9 Different Types of Agate
1. Fortification Agate
Fortification agates are the classic agate: striped, colorful, and generally forming rings. The “fortifications” are enclosed bands that wrap around inside the nodule as the stone separated into different layers during its formation.
Fortification agates are fairly common and they make up the collections of many collectors. The key is in finding and identifying the rare stuff, such as Fairburn Agates, and separating it from the rest of the material in an area.
Fortification agates are often left in their rough form or simply tumble-polished. The best are often split into display specimens, and they’re often more valuable that way instead of continuing to process the stone into cabochons.
In the US, there is a wide range of fortification agates. Much of the most sought-after material occurs in the Great Lakes area, but nodules are spread from coast-to-coast.
2. Moss Agate
Moss agate is a personal favorite of mine, with inclusions that look like moss inside the chalcedony. The best specimens will have multiple colors with a pleasing pattern in clear chalcedony, less impressive specimens can be found with single-colored moss or lower clarity as well.
Moss agate is relatively popular and easy to find in raw, tumbled, or cut forms online. It’s a common find in many places, but moss agate varies widely in appearance.
Dendritic agate also falls under this umbrella, having a similar pattern but less clarity in most cases. The inclusions resemble small branches or trees, but the appearance of the inclusion is usually black.
Moss agate can come in a wide variety of colors other than green. While green moss agate is quite common there are many different oxidized metals that can end up forming in chalcedony. Still, iron and copper make up the bulk of it with orange or green colors depending on the element of the metal.
3. Plume Agate
Plumes are a bit different than moss, although the similar look can make them a bit confusing. For the most part, plume agate will resemble feathers or smoke instead of moss. Coloration depends largely on what metallic compound creates the illusion.
Plumes are one of the more complex forms found inside agates, and there are dozens of distinct varieties. The mineral inclusions can be complex or singular, depending on the locality or even the individual agate nodule. Plumes are, quite often, multicolor as well.
Plume agates are among the most common to find themselves cut into forms for jewelry. The beautiful, unique forms make each piece different, regardless of the design of the metal. It’s all about the unique plumes that make up each stone, creating a huge variety of differences even in the same location.
4. Tube Agate
Tube agates are another example that has a wide range of coloration and value. Turkish Tube Agate is famous, but there are other awesome examples of this variation of agate formation.
Tube agates had mineral tubes or sticks forming in them during the period when they were underground. At that stage, agates are only a silica-rich gel before pressure and time create the stones we know and love. These tubes can either be filled in with silica later or remain as the original mineral formation.
The end result is tubes and sticks that show up in the agate, both on the surface and after they’ve been cut. Picking the correct angle to cut is important as the view of the tube inclusions will depend entirely on where they’ve been cut.
5. Iris Agate
Iris agates appear to be mostly transparent chalcedony with a bit of white banding. At first glance they’re often not very impressive, especially before they’ve been cut and revealed their optical effect. Once that happens, however, they can be downright breathtaking.
Iris agates display a rainbow of colors throughout their tight bands when light hits at the right angle. This is perpendicular to the banding but not necessarily the stone. An individual specimen may be a bit off due to the way it’s been cut. The mechanism is simple diffraction rather than a schiller effect or iridescence like that seen in opals.
Iris agate is sometimes used in jewelry but only displays well in earrings due to the nature of the optical qualities. It most often finds itself in lighted displays or just collectible specimens which are observed on their own. Regardless of the end-use… Iris Agate is a visual wonder when viewed from the correct angles.
6. Fire Agate
Fire agate is one of the most spectacular, and valuable, varieties of agate. The inclusions take the form of botryoidal formations of iridescent minerals inside of clear chalcedony. It’s one of the most expensive agates in the world, especially high-grade finished pieces meant for jewelry.
These formations are fractions of a millimeter thick, making fire agate much trickier to cut properly than most agates. It remains just as hard as the rest, but working your way carefully down to the formation is required to preserve the form and color play of the stone.
Fire agates are found in New Mexico, Arizona, and California. While limited, there are quite a few places you can dig for it. Including paid digs if you prefer. Either way, the digging is in the desert, so you should be prepared for hot weather to go with your hot finds.
7. Eye Agate
Eye agate has orb-shaped inclusions that often end up being cut and resembling… an eye. It’s cool stuff, and there’s a lot of variance in how it forms. A good way to describe it is as fortification agate… contained within agate.
Eye agate is different than tube agate which is cut perpendicular to the tubes. Eye agates are often in chalcedony that doesn’t have much transparency, leading to a background bordering on opaque with a speckled appearance.
Eyes can occur in many agates, but some areas like Botswana are known to host more of them. You can even find eyes in varieties of chalcedony like Carnelian if you get lucky! Each eye agate is unique, and that’s half the fun.
8. Seam Agate
Seam agate is simply agate that is formed in the seam between mineral layers instead of in round nodules. It can be any variety of agate, but a lot of it is simple waterline agate that has formed in veins.
Seam agates aren’t found as often by collectors, since you generally have to knock apart some stone to get good samples. On the other hand, in some areas, you can find them where long seams have been eroded and passed into a river.
Seam agate is known for intense coloration, with many amazing samples coming out of Turkey. On occasion, you can even find them with quartz crystal growth in the center, creating a transparent layer in the center of the amazing colors.
9. Waterline Agate
Waterline agate consists of different layers of colored chalcedony, often contained within a nodule of less well-formed agate. These agates only have horizontal stripes, as opposed to the complete bands of fortification agate, and can have many layers with different colors.
This banding can be made into cabochons or cameos, but often it’s only part of the display of a larger specimen. Waterline agate tends to not have vivid colors. It comes in light blues and earth tones. That’s definitely not the case every time, however, and there are some vivid reds and oranges to be found.
Waterline agate remains popular with carvers and collectors around the world. A good specimen is amazing on the shelf, and it can be cut using the visuals of the stone to great effect. They’re always a nice surprise when you pull them off the saw!