Agate is in the quartz family; more specifically it is a form of chalcedony quartz. Agate is most commonly used as a name for chalcedony that is banded, and the variety of colors and patterns that can be found in Agates is endless, although sometimes the term is also used for non-banded stones. Due to the many varieties, there are often specific names for different variations of this gemstone (including some which aren’t banded), which can cause confusion for those not in the gemstone trade.
Etymology & Sources
Agate gets its name from the ancient Greeks, who named it after the river Achates in Italy (now known as the Dirillo River), where it was first discovered. Deposits can be found in many places across the world, and thanks to this it is relatively common and very affordable.
Agate can be found in virtually any color and pattern, and in this sense each individual Agate gemstone can be seen as unique. Agates which are not banded and are single-colored often have alternate names. The gemstones can range from translucent to Opaque, and normally has a dull or waxy luster. Agates are most commonly cut as cabochons to emphasize the banded patterns and enhance beauty. Due to the structure and commonness of Agate of all varieties, very large stones can be cut – this also allows for carvings and statuettes to be made from the material.
Agate is a form of quartz and like other quartz varieties is relatively hard. This, combined with its affordability makes Agate a durable and also replaceable stone that is suitable for use in any jewelry. Agate has the typical density of any quartz, roughly 2.6 on the Specific Gravity scale, and has a Refractive Index on about 1.54.
Agate is common enough and hard enough to be suitable for virtually all decorative purposes, including jewelry of various kinds as well as ornamental statuettes and carvings. It is particularly popular as a gemstone for use in men’s jewelry and is great for ‘earthy’ or ‘tribal’ designs in charms, anklets, or pendants.
Due to the large variety of trade names for Agates of different appearance and from different sources, it is impossible to list them all in one place. We have attempted to include the most common trade names and varieties of Agate here:
- Carnelian – Carnelian (red/brown chalcedony) that has bands can also be considered a form of Agate
- Dendritic Agate – Technically is not an Agate as it has no bands. Translucent grey or white chalcedony variety with plant-like inclusion patterns.
- Eye Agate – Agate with perfectly round banded rings that often resemble eyes.
- Fire Agate – Agate with play of color (like that seen in Opals), will sheen with multiple colors.
- Moss Agate – Agate with heavy green inclusions that resemble its namesake. Similar to Dendritic Agate in that it is technically not an Agate as it lacks banding.
- Sard – Essentially the same as Carnelian except darker brown or red – when it has bands it can be considered an Agate also.
- Sardonyx – An Agate that has brown or red bands combined with either white or black bands.
- Onyx – Black Chalcedony variety, when it has bands it can be considered a form of Agate.
Agate is sometimes dyed to improve the intensity of color, but either way Agates should be very affordable.