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Chalcedony Gemstone Information

About Chalcedony - History and Introduction

Chalcedony is a gemstone species which belongs to the quartz group of minerals. Technically, chalcedony is the gemological term applicable for all varieties of quartz in cryptocrystalline form, which can occur in a wide range of different colors, sizes and patterns. However today, the term, 'chalcedony', is most often used in reference to a very specific type of cryptocrystalline quartz, often referred to as 'actual chalcedony' or 'chalcedony in the narrow sense'. Fortunately, to minimize confusion, most other varieties of cryptocrystalline quartz are traded under their own individual trade names, such as 'banded agate', 'carnelian' or 'jasper'. The gemstone 'chalcedony' is distinguished by translucency and its solid, lighter color, typically ranging from bluish to white or gray.

Cryptocrystalline quartz is a compact to dense form of silica, which means it has extremely fine crystallization. In fact, most cryptocrystalline crystals are so fine that distinct particles cannot even be seen under a microscope. Some cryptocrystalline material may be sub-classified as 'microcrystalline', which refers to cryptocrystalline material with slightly larger crystals (discernable when sliced thinly and observed under a polarizing microscope).

For most of time, chalcedony was thought to be a 'fibrous' variety of cryptocrystalline quartz, but more recently it was actually discovered to be a combination of quartz and another silicate mineral; moganite (a polymorph of quartz). Both quartz and moganite share the same silicon dioxide chemical composition, but they have varying crystal structures. Moganite is monoclinic, while traditional quartz belongs to the trigonal crystal system. Chalcedony forms with a hexagonal crystal structure.

As the defining mineral for 7 on the Mohs scale, chalcedony quartz is known to set the standard when it comes to gemstone hardness for jewelry gemstones. The actual name 'chalcedony' originated from the latin word 'Chalcedonius', which is thought to be derived from 'Chalcedon', an ancient seaport of Asia Minor, now Kadikoy, Turkey. Chalcedony is known to take an excellent polish, in fact, after a prolonged polish, some chalcedony varieties can exhibit a glow that seems to emanate from within. Chalcedony quartz is without a doubt one of the most significant materials of all time, not only for the jewelry industry, but it is an important material for various scientific and industrial uses as well.

Chalcedony Quartz
Chalcedony
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Identifying Chalcedony Back to Top

Chalcedony quartz can typically be identified from other minerals through its composition (silicon dioxide), hexagonal crystal structure and superior hardness. Chalcedony is also known to possess slight piezoelectricity, similar to that of tourmaline, which means it can carry a small electrical charge. Surprisingly, as common as quartz is, there are actually very few materials that can be easily mistaken for chalcedony.

Although distinguishing chalcedony quartz from other minerals is quite easy, identifying individual varieties from within the chalcedony group can be very difficult, as this requires precise observation of color, patterns, impurities and even localities. Another factor which makes identifying chalcedonic varieties even more difficult is that many specimens can fall under multiple trade names.

Some of the most popular 'official' chalcedony varieties are identified as follows:

Agate: Agate is distinguished by having multiple colors. Some can occur in solid colors, such as green and black, but most of the stones available on the market today have been dyed to obtain their color. There are countless varieties of agate available, with banded agate being the most popular and well known agate variety. One of the rarest types of agate is 'fire agate', which exhibits an iridescent property, reflecting colors of red, gold, green and blue-violet. Other popular agates include agate jasper, agate geode, dendritic agate, tree agate, 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.

Bloodstone: Bloodstone is an opaque, dark-green chalcedony with red to brown spotting caused by iron oxide. Some may exhibit yellow spotting, which is known as 'plasma' in the gem trade.

Blue Chalcedony: Sometimes called "Mohave" and "Mt. Airy blues", originating in California and Nevada, these are a slight to moderate grayish blue color, ranging from a light to medium color intensity. Blue chalcedony from Namibia, often called "African blue", ranges from grayish to nearly pure blue and from light to medium dark. The most valuable blue chalcedony is sourced from Oregon, USA. Its blue color is slightly modified by traces of pink, resulting in a noticeably lavender gemstone, which is nonetheless referred to as "holly blue."

Onyx: Onyx is a layered stone with a black base and a white upper layer. Uni-colored chalcedony is sometimes called onyx.

Carnelian: Carnelian ranges in color from yellow-orange to rich, near-reddish orange to orangey brown. It can also vary from semi-opaque to highly translucent. 'Cornelian onyx' is a layered stone with a red base and a white upper layer.

Chrysoprase: Chrysoprase is an apple-green chalcedony that derives its color from nickel, ranging from nearly opaque to nearly transparent. Its color spectrum includes olive color to near-pure greens of medium tone. Very fine, highly saturated pieces are often misrepresented as 'imperial jade'.

Chrysocolla chalcedony: Chrysocolla chalcedony is marketed as 'gem silica', which is one of the most valuable and rare varieties of chalcedony. It is distinguished by its soft blue to blue-green color. Gem silica can occur from opaque to near transparent, with transparent materials being most valuable. Its coloring agent is copper.

Petrified wood: Petrified wood (also called fossilized wood) is fossilized organic remains which have undergone a petrification process. Typically, the organic remains are replaced by chalcedony minerals, resulting in a very intriguing and attractive wood-like gemstone which can take an excellent polish. Arizona is the most well-known commercial source, particularly the privately owned lands of the Navajo and Apache tribes near 'Petrified National Forest'. Petrified wood is suitable for any type of jewelry, as well as polished objects of art and ornamental carvings.

Chalcedony Origin and Gemstone Sources Back to Top

Chalcedony is compact silica most often found in sedimentary and volcanic environments. Formation occurs over a long period of time, as minerals are slowly deposited into a pocket of another type of rock, such as granite. Areas that host volcanic activity frequently harbor the most abundant chalcedonic deposits. In many cases, silicon dioxide forms in sometimes readily visible and parallel bands, as seen in banded agate. However, with most materials, the separate deposits appear blended or cloudy to the eye, as with carnelian, moss agate and 'actual chalcedony'.

Although some regions are better known than others, high quality chalcedony deposits can be found all over the world. Almost all of the United States is known to produce chalcedony. Other notable sources for the lighter, translucent and bluish 'actual chalcedony' material include Uruguay, India, Madagascar, Myanmar (Burma), Mexico, Brazil and Southwestern Africa.

Below are some more detailed notable sources for specific varieties of chalcedony:

Australia: Agate, chrysoprase, bloodstone
Brazil: Agate, chalcedony, bloodstone, chrysoprase
China: Agate, bloodstone
India: Agate, chalcedony, bloodstone, carnelian, chrysoprase
Kazakhstan: Chrysoprase
Madagascar: Agate, chalcedony, chrysoprase
Mexico: Agate
Mongolia: Agate
Namibia: Agate, blue chalcedony, chalcedony,
Russia: Chrysoprase
Sri Lanka: Chalcedony,
Uruguay: Agate, chalcedony,
South Africa: Chrysoprase
Tanzania: Chrysoprase
Zimbabwe: Chalcedony, chrysoprase
USA: Agate (Montana and Wyoming), chalcedony (California), chrysocolla, chalcedony, petrified wood (Arizona), bloodstone, blue chalcedony (California, Nevada, Oregon).

Buying Chalcedony and Determining Chalcedony Gemstone Value Back to Top

Chalcedony Color

Chalcedony can technically refer to any translucent, cryptocrystalline quartz with a single color, but in the gem trade, it is primarily used to refer to specimens with light bluish, white or gray color. The most common colors for 'chalcedony in the narrow sense' include blue-white, buff, light tan, gray, yellow, or brown. Chalcedony owes its color to quartz impurities, most often including iron, nickel, copper and or titanium.

Chalcedony Clarity and Luster

Chalcedony occurs translucent to opaque, with translucent materials being more desirable. It has an attractive luster when cut and polished, often appearing waxy or vitreous to dull. Generally, chalcedony is often milky with obscured color. The cloudy distribution is a good indication of authenticity and as long as translucency is not affected, the milky clarity does not significantly affect the overall value. Chalcedony often has visible inclusions which in most cases are considered acceptable.

Chalcedony Cut and Shape

Chalcedony is typically cut en cabochon. Cabochon style cutting accentuates the desirable glow for which it is prized. On rare occasion, exceptionally transparent material may be faceted. The most popular shapes include oval, round and cushion, but they are also commonly fashioned with fancy shapes, such as trillions, hearts and flower-cuts. Tumbled stones and drilled beads are very popular, especially owing to chalcedony's durability. Chalcedony is an ideal material for gemstone carvings, including cameos, seals, insignia and ornamental figurines.

Chalcedony Treatment

Chalcedony is occasionally color-enhanced through dyeing. Irradiation is not very common, but is not unheard of. Chalcedony can also be heated, but heating will often yield reddish materials. Heating, irradiation and dyeing are not very common for 'actual chalcedony', but are performed on other varieties of chalcedony. Actual chalcedony is typically left untreated and unenhanced throughout production from the mine to the market. Chalcedony is considered to be quite porous, which allows it to be easily dyed to imitate other gems. In most cases, dyeing is not done with the intention to imitate another gem type, such as turquoise or howlite, however, it is done to replicate a specific variety of itself, such as carnelian or banded agate. In addition to dyeing, some materials may have been bleached to help achieve desired colors when dyeing.

Chalcedony Gemological Properties: Back to Top
Chemical Formula: SiO2 - Silicon dioxide
Crystal Structure: Hexagonal
Color: Bluish, white, gray, purple, lavender, light-tan, yellow and brown
Hardness: 6.5 to 7 on the Mohs scale
Refractive Index: 1.530 to 1.540
Density: 2.58 to 2.64
Cleavage: None
Transparency: Translucent, opaque
Double Refraction or Birefringence: Up to 0.004
Luster: Waxy, dull or vitreous
Fluorescence: Blue-white

Please refer to our Gemstone Glossary for details of gemology-related terms.

Chalcedony: Related or Similar Gemstones: Back to Top
Blue Dumortierite Quartz
Dumortierite Quartz

Chalcedony belongs to the very large group of quartz minerals. Quartz is one of the most abundant minerals, second only to the feldspars. Considering the abundancy of quartz minerals, there are numerous similar and related 'chalcedony' and 'actual chalcedony' gemstones. In fact, there are so many unofficial trade names today for varieties of chalcedony, that it's almost impossible to list them all, especially since new names pop up often and new varieties are continuously being 'discovered', most of which are simply locality based names, often dependent on the exact mining location.

For the most part, unofficial regional trade names are used only by the most serious of gem collectors, while officially recognized trade names are commonly used by the gem industry, which minimizes confusion and conflict.

Most Popular Related Chalcedony Gemstone Trade Names:

Agate, jasper, onyx, carnelian, cat's eye quartz, golden quartz (also known as 'lemon quartz'), beer or whiskey quartz, mystic quartz, rose quartz, tiger's eye, agate geode and aventurine are some of the most popular and well-known related varieties of chalcedony.

Lesser-Known Related Chalcedony Gemstones Trade Names:

Blue Quartz, chrysocolla, chrysoprase, prase, fire agate, sard, sardonyx, plasma, chrome chalcedony (mtorodite), cornelian onyx, hawk's eye, prasiolite, dumortierite quartz, tiger's eye matrix, chrysocolla chalcedony (gem silica) and dendritic agate are some of the lesser-known related varieties of chalcedony.

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

Chalcedony has been one of the most treasured gemstones throughout many ancient civilizations. It is believed that as early as the Bronze Age, chalcedony was prized as a gem throughout areas surrounding the Mediterranean, owing to the discoveries of archaeologists. Many chalcedony seals and other forms of jewelry and fabricated tools have been discovered dating back as early as 1800 BC. Chalcedony has been used and prized by ancient Romans, Greeks, Babylonians and Assyrians alike. Many Native American tribes consider chalcedony to be sacred and most often use it in traditional ceremonial gatherings, particularly in efforts to stabilize and strengthen the bonds between tribes.

Onyx, a popular variety of chalcedony, is the official modern birthstone for December and it is also the official zodiac stone for Leo. Another chalcedony, known as carnelian, is the official stone for Virgo. Chalcedony is believed to help emotional balance and it is thought to be able to strengthen stamina and endurance. It encourages kindness, responsiveness, receptivity, generosity, charity and friendliness in those who wear it. It is also thought to possess the unique ability to balance all of the energies of the body, mind and spirit. Physically, chalcedony quartz is used to heal and alleviate symptoms of fever, leukemia and various eye illnesses.

Disclaimer: Metaphysical and Alternative Crystal Healing Powers and Properties are not to be taken as confirmed advice. Traditional, Ceremonial and Mythological Gemstone Lore is collected from various resources and is not the sole opinion of SETT Co., Ltd. This information is not to replace the advice of your doctor. Should you have any medical conditions, please see a licensed medical practitioner. GemSelect does not guarantee any claims or statements of healing or astrological birthstone powers and cannot be held liable under any circumstances.
Chalcedony Gemstone and Jewelry Design Ideas Back to Top

Chalcedony is one of the most important jewelry and ornamental stones of all-time. Unlike many other colored stones, chalcedony can often be found in local jewelry stores, especially common varieties like agate, carnelian and onyx. It is a favorite for both hobbyists and professional jewelers, owing to its affordability, abundance and variety of glowing translucent tones, colors, shapes and patterns. Month after month, many of the most elite jewelry magazines, such as Modern Jeweler, Lapidary Journal, and Metalsmith feature exquisite chalcedony gemstone jewelry.

Chrysoprase, an apple-green variety of chalcedony, and rare 'gem silica' are the most valuable chalcedony varieties. They can easily command extremely high prices and are often set into high-end designs. 'Actual chalcedony' has only recently become popular for use in gemstone jewelry, although it has been used for centuries for decorative arts and traditional jewelry. All chalcedony quartz is perfectly suitable for any type of jewelry design imaginable, including pendants, necklaces and even daily-wear gemstone rings. Chalcedony has the durability and hardness required for mainstream jewelry, making it very resistant to wear-and-tear. It can be classy, traditional, urban or tribal depending on how you wear it and it rarely requires any special maintenance. Chalcedony is a favorite for both men and women owing to its versatility.

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 diamond by weight in comparison.

Gemstone Caring and Cleaning for your Chalcedony and Gemstone Jewelry Back to Top

How to clean your gemstonesChalcedony is a variety of quartz. All quartz is considered quite durable compared to most other gemstones. Chalcedony can be easily cleaned using warm, soapy water and a soft cloth or brush. Be sure to rinse well to remove any soapy residue. Even though quartz has excellent hardness and durability, there are still a variety of other materials easily capable of scratching chalcedony, including diamond, sapphire, spinel and topaz. Avoid storing mixed gems together, whether softer or harder, in order to prevent scratches and fractures to your gemstones and jewelry.

As with most gemstones, avoid the use of any harsh household chemicals (bleach, sulfuric acid etc.) when caring for or cleaning chalcedony. Chalcedony is quite porous, which means that it can be easily stained and absorbs chemicals and colors very easily. Avoid prolonged exposure to extreme heat, as heating quartz can permanently alter the color of your gemstones. When storing chalcedony gemstones, wrap them using a soft cloth and place them inside a fabric-lined box for added protection. Always remove gems and jewelry before exercising or playing any sports.

  • First Published: September-25-2006
  • Last Updated: July-04-2014
  • © 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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