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History & Introduction


For the creation of spring jewelry chalcedony is considered to be an excellent gemstone. It is available in silky light-blue color and is delicate in nature, it reminds of early morning mountain sky. Its name is said to come from an ancient Greek town called Chalkedon, now in Turkey. This gemstone possess the property of fine-grained variety of quartz with a luster that is waxy and microscopic compressed crystals. Due to this structure, chalcedony is mainly semi-opaque that gives a soft glow when the light diffuses through the stone. It is perfect for graceful jewelry.

The Romans used chalcedony to make seals and the stone is carved into ornaments for ages. In the past its heavenly blue color give reason that why it was called Mecca stone and St Stephen's stone.

Chalcedony comes from the quartz group of minerals. According to technical view chalcedony is the gemological term applicable for every kinds of quartz in cryptocrystalline form that occurs in a wide range of colors, sizes and patterns. Currently, the term, 'chalcedony', is maximum used in reference to a very specific type of cryptocrystalline quartz, often referred to as 'actual chalcedony' or 'chalcedony in the narrow sense'.

Cryptocrystalline quartz is a compact to dense form of silica that shows it has extremely fine crystallization. Indeed, maximum cryptocrystalline crystals are so fine that it is not possible to see distinct particles under a microscope. Few of the cryptocrystalline material are sub-classified as 'microcrystalline' that refers to cryptocrystalline material with slightly larger crystals (discernable when sliced thinly and observed under a polarizing microscope).

The real name 'chalcedony' originated from the latin word 'Chalcedonius' that is thought to be derived from 'Chalcedon', an ancient seaport of Asia Minor, now Kadikoy, Turkey. Chalcedony is famous to take a perfect polish, actually, after a prolonged polish, some chalcedony varieties show a glow, which seems to emanate from within.

Recognise - Naturally, chalcedony quartz is identified from other minerals because of its composition (silicon dioxide), superior hardness and hexagonal crystal structure. Chalcedony is even known to possess slight piezoelectricity, just like tourmaline that shows it can carry a small electrical charge. Unexpectedly, as common as quartz is, there are actually some materials available that are easily mistaken for chalcedony.

In fact discerning chalcedony quartz from other minerals is easily possible, recognizing each varieties from within the chalcedony group is very difficult, as this needs accurate observation of color, patterns, impurities and even the area. Another factor that helps to identify chalcedonic varieties is even more difficult, it is with many specimens that fall under multiple trade names.

Some of the most popular 'official' chalcedony varieties are-

Agate: Agate is differentiated with multiple colors. Some are available in solid colors like green and black, however maximum stones available on the market currently are dyed to obtain their color. 'Fire agate', other popular agates are jasper, geode, dendritic, tree, Botswana, blue lace, fossil, iris, laguna, landscape, scenic, tube, snakeskin, Sweetwater, Mohave blue, thunder egg, Fairburn, Dry head and Lake Superior.

Bloodstone: Bloodstone is opaque by nature, the chalcedony in dark-green color including red to brown spotting.

Blue Chalcedony: The color is from grayish blue, ranging from light to medium color intensity. Blue chalcedony comes from Namibia and is also called "African blue", it ranges from grayish to nearly pure blue and from light to medium dark.

Onyx: Onyx is available in layers with a black base and a white upper layer. At times uni-colored chalcedony is called onyx.

Carnelian: Carnelian gemstone is available in color from yellow-orange to rich, near-reddish orange to orangey brown.

Chrysoprase: It is an apple-green chalcedony, which gets the color from nickel, ranging from nearly opaque to transparent.

Chrysocolla chalcedony: This gemstone is one of the most valuable and rare varieties of chalcedony. It is differentiated by its soft blue to blue-green color.

Petrified wood: Petrified wood (also called fossilized wood) is fossilized organic remains that undergo a petrification process. Naturally, the organic remains are replaced by chalcedony minerals that results in a very interesting and attractive wood-like gemstone.

Availability - Chalcedony is a compact silica mainly it is found in sedimentary or volcanic environments. Though, some regions are better known than others, excellent quality chalcedony deposits are found across the globle. Almost all of the United States is known to produce chalcedony. Besides for the lighter, translucent and bluish 'actual chalcedony' material the sources are Uruguay, India, Madagascar, Myanmar (Burma), Mexico, Brazil and Southwestern Africa.

Mentioned are the specific varieties of chalcedony availability:

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).

Usages - If you design handcrafts, try making matching chalcedony earrings and a bracelet. Small beads with subtle silver spacers for style. It is sold in a white or light-blue box. It is accepted that chalcedony quartz is one of the most significant materials of all time. It is not only used in jewelry industry, however it is also an important material used for various scientific and industrial uses as well.

Buying Guide

Color - Technically, chalcedony is referred to any translucent, cryptocrystalline quartz along with a solo color, however in case of gem trade, mainly it is used to refer for specimens with light bluish, white or gray color. Commonly used colors for 'chalcedony in the narrow sense' is available in light tan, blue-white, yellow, buff, gray or brown. Chalcedony gets color from the impurities of quartz mainly it includes iron, titanium, nickel and copper. Chalcedony is available every color, however in case of jewelry it's usually light milky blue with a hint of pink. Due to porous nature, it is dyed blue and pale minty-green for centuries - and at times its color improve to emerald green and even tangerine and peachy pink.

Clarity and Lustre - Chalcedony appears to be translucent to opaque, with translucent materials, which more in demand. It possess attractive luster once it is cut and polished, maximum time it appears to be waxy or vitreous to dull. In general, chalcedony is often milky with hidden color. The cloudy distribution is a good indication of validity as long as the translucency remains unaffected, the milky clarity does not significantly affect the overall value. Chalcedony mainly shows visible inclusions that in maximum cases are considered acceptable.

Cut and Shape - Naturally, chalcedony is cut en cabochon. Cabochon style cutting highlights the glow that is in demand and which it is prized too. Rarely, very transparent materials are faceted. Maximum popular shapes available are cushion, oval and round, however they are also commonly fashioned with fancy shapes like flower-cuts, trillions and hearts. Drilled beads as well as tumbled stones are very popular, particularly owing to the durability of chalcedony. Chalcedony is an ideal material for gemstone carvings that adds up to ornamental figurines, cameos, seals and insignia.

Treatment - Rarely, chalcedony is color-enhanced with dyeing. Irradiation is not very common, but still in use. Chalcedony is heated, however heating will maximum time yield reddish materials. Heating, dyeing and irradiation are not very common for 'actual chalcedony', however they performed acted on different varieties of chalcedony. Actual chalcedony is naturally left untreated and unenhanced totally in production from the mine to the market. Chalcedony is actually quite porous that allows it to be easily dyed to imitate various gems. In maximum cases, dyeing is not done just to imitate different gem type like turquoise or howlite, but it is done to replicate a particular variety of itself like carnelian or banded agate. Including dyeing, some materials may have been bleached to help achieve desired colors when dyeing.

Gemological Characteristics:

Chemical Formula SiO2 - Silicon dioxide
Crystal Structure Hexagonal
Color Bluish, purple, lavender, light-tan, yellow white, gray and brown
Hardness From 6.5 to 7
Refractive Index From 1.530 to 1.540
Density From 2.58 to 2.64
Cleavage Not found
Transparency Translucent, dull
Double Refraction / Birefringence Up to 0.004
Lustre Waxy, dull or vitreous
Fluorescence Blue-white
Streak White
Crystal Forms and Aggregates Chalcedony, is a microcrystalline variety of the mineral Quartz, is not found in visible crystals. It is available in botryoidal, mammilary, stalactitic, massive, nodular forms, as smooth rounded pebbles, as banded masses, as amygdules, and as the linings of geodes.
Fracture Conchoidal
Tenacity Brittle
Rock Type Igneous, Sedimentary, Metamorphic
Popularity (1-4) 1
Prevalence (1-3) 1
Demand (1-3) 1

Classification:

  • Blue chalcedony
  • Pink chalcedony