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Informazioni e consigli sull'agataАгат информация

Agate Gemstone Information

About Agate - History and Introduction

Agate belongs to the quartz (silicon dioxide) family of minerals. Quartz is the second most abundant mineral found on earth’s continental crust, second only to the feldspar mineral group. Quartz is distinguished and separated into two main branches: macrocrystalline quartz and cryptocrystalline quartz.

Agate is classified under the cryptocrystalline variety and more specifically, as a variety of chalcedony quartz. Cryptocrystalline specimens crystal structures are so fine, they cannot be seen - even with the aid of a microscope. Agate is often referred to as being ‘microcrystalline’; this term merely suggests that the crystal structure is 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.

Agate Gemstone
Identifying Agate Back to Top

Cryptocrystalline quartz is broken down into fibrous and granular varieties. The fibrous varieties are referred to as chalcedony quartz. Chalcedony quartz can occur in a wide range of colors and patterns. Agate is traditionally defined as the ‘banded’ variety of chalcedony quartz, whereas lighter and solid-colored specimens are referred to as simply ‘chalcedony’. There are many different 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 ‘sardonx’, 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, ‘Achates’ (Greek: Aχάτης). The Achates River is located in Sicily, Italy, but the river has been renamed and is now known as the Dirillo River since then.

Agate stones available on the market today, originate from deposits all over the world including Myanmar, Brazil, Uruguay, Argentina, Mexico, Botswana, India, Australia and the USA.

Agate is usually found alongside numerous other types of rock, but it is primarily classified as volcanic rock. Agates frequently form within pockets of igneous, sedimentary and metamorphic rock such as granite, melaphyre and porphyry. Deposits of silicon dioxide typically form in almond or ball-shaped nodules and as the deposits continue to build over long periods of time, parallel bands are created through the process. Banded specimens are referred to as agate, while uniform and blended species are classified as chalcedony, carnelian, moss agate or other specific trade names.

Buying Agate and Determining Agate Gemstone Value Back to Top

Agate Color

Agate occurs in wide range of colors and patterns. Although some colors occur more commonly than others, almost all agate will be multicolored due to unique banding. Single-colored agates can occur naturally, but most of the stones available today have been dyed to obtain unicolor. Single-colored agates are often traded using specific trade names, such as sard and carnelian. Agate colors can include black, white, blue, red, green, yellow, orange, brown, pink, purple and gray.

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.

Agate Clarity and Luster

Cryptocrystalline quartz is typically distinguished from macrocrystalline quartz by clarity and luster; cryptocrystalline clarity typically ranges from translucent to opaque and luster will most often be waxy or dull like agate and chrysocolla. On the other hand, macrocrystalline quartz is typically transparent to translucent and with vitreous luster like amethyst, citrine and rose quartz.

Agate Cut and Shape

Agates can be found in very large sizes and in a variety of shapes. Most agates are cut en cabochon to enhance their beauty, but they are also found in free-form slabs and plain cuts. They are also commonly used for ornamental designs such as cameos and other carvings.

Agate Treatment

Agate is typically untreated but can easily be dyed to enhance color since it is quite porous. Prices for agates are very affordable whether they have been dyed or not. Regardless, sellers should always disclose any and all treatments to the best of their knowledge.

It is very difficult to test agate for dyeing without breaking the stone. Most gem labs lack the proper equipment to do so. Agate is a popular choice for beading and tumbled jewelry. Most tumbled and agate beads are dyed to enhance color. Bright unicolor agates, especially those from Brazil, are typically dyed although untreated specimens do exist.

Agate Gemological Properties: Back to Top
Chemical Formula: SiO2 - Silicon dioxide
Crystal Structure: Cryptocrystalline - microcrystalline aggregate (trigonal)
Color: All colors, multicolored and banded
Hardness: 6.5 - 7 on the Mohs scale
Refractive Index: 1.530 - 1.540
Density: 2.60 - 2.64
Cleavage: None
Transparency: Translucent to opaque
Double Refraction / Birefringence: Up to 0.004
Luster: Waxy - dull
Fluorescence: Varied based on bands: Yellow, green, blue-white; slightly strong
Agate Gemstone Varieties or other Similar Gemstones: Back to Top
Carnelian gems for sale
Carnelian

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:

Most Popular Agate Varieties:

Banded agate, carnelian, sard, sardonyx, onyx, chrysocolla, eye agate, dendritic agate, fire agate, agate geode, moss agate and brecciated agate

Lesser Known Agate Varieties:

Tree agate, agate jasper, Botswana agate, blue lace agate, fossil agate, iris agate, laguna agate, landscape agate, scenic agate, tube agate, snakeskin agate, Sweetwater agate, Mohave blue agate, thunderegg agate, Fairburn agate, Dryhead agate, and Lake Superior agate.

Agate Gemstone Mythology, Metaphysical and Alternative Crystal Healing Powers Back to Top

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 amulet throughout ancient times.

Agate has the ability to quench thirst and protect from fevers. Alternative healers will place agate stone on the solar plexus to alleviate stomach illnesses. Agate is a stone of strength and gives the power to move forward and carry on through tough times.

Disclaimer: Metaphysical and Alternative Crystal Healing Powers and Properties are not to be taken as confirmed advice. Should you have any medical conditions, please see a licensed practitioner. This information is not to replace the advice of your doctor. GemSelect does not guarantee any claims or statements made and cannot be held liable under any circumstances.
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.

Agate is ideal for just about any type of jewelry design imaginable. They can be worn as a pendant, necklace or as an everyday ring. Agate is harder than most other material, and so it is very durable and resistant to wear and tear. Agates are a favorite among men because of the abundance of sizes and shapes available. Some of the fancy free-form shapes are very unique and can provide a tribal look that many gentlemen prefer, making especially unique pendants. Agates are also an excellent stone for ladies as well. Many wonderful charm bracelets and beaded anklets will utilize agates as the main stone of choice.

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

How to Clean your GemstonesAgate 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: May-12-2014
  • © 2005-2014 GemSelect.com all rights reserved.
    Reproduction (text or graphics) without the express written consent of GemSelect.com (SETT Company Ltd.) is strictly prohibited.
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