Agate Gemstone Information
About Agate - History and Introduction
Agate belongs to the quartz (silicon dioxide) family of minerals. The quartz group is the second most abundant mineral found on earth’s continental crust, second only to the feldspar mineral group. All quartz gemstones share the same silicon dioxide chemical composition, but are distinguished and separated into two main branches based upon differing crystal classes and formations. The two main branches of quartz include macrocrystalline quartz and cryptocrystalline quartz; agate belongs to the latter. More specifically, agate is a variety of chalcedony, which includes a wide range of other gemstones, including chrysoprase, bloodstone, jasper and carnelian.
Cryptocrystalline quartz exhibits crystal structures so fine, they cannot be seen, even with the aid of a microscope. Agate is often referred to as being microcrystalline, which merely suggests that the crystal structure is just slightly larger than most other cryptocrystalline species. The difference between micro and cryptocrystalline is not clearly defined, so it would not be considered incorrect to describe agate as either. Macrocrystalline quartz is typically transparent to translucent and forms with larger crystals than cryptocrystalline quartz. Macrocrystalline gemstones include amethyst, citrine, hawk's eye, smoky quartz, rose quartz and tiger's eye.
Identifying Agate Back to Top
Cryptocrystalline quartz is broken down into fibrous and granular varieties; fibrous varieties are referred to as chalcedony quartz. Chalcedony occurs in a wide range of colors and patterns. Agate is traditionally defined as a ‘banded’ variety of chalcedony, whereas lighter and unicolored specimens are referred to as simply, chalcedony. There are many varieties of agate available, making shopping for agate very confusing for most consumers. This is because stones will commonly be referred to using specific trade names, such as 'banded agate', 'carnelian' and 'sardonyx', while simultaneously traded as just chalcedony, chalcedony quartz or even plain quartz.
Agate Origin and Gemstone Sources Back to Top
Agate was first discovered sometime around the 3rd or 4th century (BC) by Theophrastus, a Greek philosopher who named the stone after the river in which it was found; the ‘Achates’. The Achates River is located in Sicily, Italy, but the river has been renamed and is now known as the Dirillo River. Agate can originate from countries all over the world, including Myanmar, Brazil, Uruguay, Argentina, Mexico, Botswana, India, Australia and the USA. In general, South American agate stones lack any special markings. They will also typically occur in a rather dull gray color. Agates from the once plentiful mines of Idar-Oberstein in Germany, which are now depleted, were well-known for their vivid and strong colors, especially natural pink, red and brown.
Buying Agate and Determining Agate Gemstone Value Back to Top
Agate Gemological Properties: Back to Top
Agate Gemstone Varieties or other Similar Gemstones: Back to Top
There are many different trade names for agate. Most are based on optical properties, but some varieties are classified based upon internal/external composition, or inclusions of other objects or minerals. Most trade names simply refer to the origin or other locational traits. These locality-based trade names are generally used only by gemstone sellers and collectors. There are some trade names which are very commonly used such as fire agate, agate geode, carnelian and onyx. Many times, a single agate specimen can be classified under two or more different trade names.
The following is a list of some common trade names used for different varieties of agate:
Agate gemstones are one of the oldest stones in recorded history. Agate is known as a stone of protection, protecting one from nightmares, stress and fatigue. Since biblical times, agates have been worn and used in jewelry to protect against imminent storms. They were highly valued as talismans and amulets throughout ancient times.
Agate Gemstone and Jewelry Design Ideas Back to Top
There are several advantages to buying loose gemstones versus preset jewelry. First off, once a gemstone has been set, it’s very difficult to know the actual quality of the stone. The jewelry setting can often hide or obscure blemishes and you may be misled into thinking the stones are better than what they actually are. You also have more variety and choice when you purchase loose gemstones. Most importantly, buying loose gemstones will save you money.
Note: Buy colored gemstones by size and not by carat weight. Colored stones vary in size-to-weight ratio. Some stones are larger and others are smaller than diamonds by weight in comparison.
Agate Gemstone and Jewelry Care and Cleaning Back to Top
Agate can be cleaned very easily using warm soapy water and a soft brush. Keeping in mind that agate is quartz and its hardness and durability, be sure to not use any other objects that are harder than agate for scrubbing or cleaning. As with most gemstones, you should not use any household chemicals when caring or cleaning your agate gemstone or gemstone jewelry pieces. Agate should avoid any prolonged exposure to extreme of heat as it may cause permanent damage to the gemstone. When storing agate, it should be stored inside a fabric-lined box or wrapped in a soft cloth. Agate should be kept away from other gemstones and jewelry to ensure unnecessary damage or scratching from other harder gemstones.
- First Published: May-30-2013
- Last Updated: October-17-2017
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