Blue Chalcedony

“I think the idea of purple and lavender chalcedony being lumped with blue chalcedony dates from the yo-yo who coined the term ‘Holly Blue,'” says gem cutter—gemologist Will Johnson, owner of Premier Gem Design in Ellensburg, Wash. Ellensburg is known for its blue—not lavender—chalcedony. Holly Blue, found in Holly, Ore., is lavender—not blue—according to Johnson. “This guy should be drawn and quartered for the confusion he’s caused. I’ve cut hundreds of pounds of Holly. None of it was remotely blue.”

And so it goes. Call a supplier and ask for blue chalcedony and they will most likely send you some stones in the purple-to-violet-to-lavender ranges, along with some true blue chalcedony. That’s because all these colors have some blue or gray that your client might appreciate. Quickly now, purple is a bluish-red. Lavender is a reddish-blue. And violet is a purplish-blue.

Chalcedony

Chalcedony is generally a translucent-to-opaque cryptocrystalline quartz. As Johnson writes, this encompasses a huge group of gem materials, including translucent-to-semitransparent single-color types, translucent-to-semitranslucent banded and pattern types (generally called agates), and opaque-pattern and single-color types (called jaspers). In common practice, however, only some of the translucent single-color types are sold as chalcedony, whereas the rest of this group is sold under individual variety names, or as jasper or agate.

Chalcedonies are nearly always cabbed or carved, although an exceptional, near-transparent piece may be faceted. Chalcedonies are tough gems, good for all jewelry applications and require no special care in wearing or cleaning.

Color and Locality

Each variety of blue has its local—and vocal—supporters. Generally, each is designated by origin. They vary in the blue’s color depth and degree of modification by gray, pink/red, or purple.

As a group they vary in tone from pale to medium, in color saturation from slight to moderate, and in transparency from semitransparent (rare) to opaque (abundant). Some of the translucent/semitransparent pieces have a slight adularescence, the moonstone effect, which enhances their value.

Johnson knows his chalcedonies and knows which regions produce which colors. For example, Mojave and Mt. Airy Blues originate in California and Nevada, respectively, and are slightly to moderately grayish-blue with slight-to-moderate color saturation. Nevada recently produced some very fine color lavender (pinkish/reddish-blue) material—though not in large sizes. Namibia’s blue chalcedony, often called “African Blue,” varies from grayish to nearly pure blue and from light to medium-dark tones. Holly Blue, arguably the most valuable of the “blue” chalcedonies, is a translucent purple-to-lavender chalcedony, that is, a blue modified by a slight-to-moderate amount of pink/red.

Theories on Color Greg Fraser, gem carver with Chan Fraser Design in Toronto, notes that chalcedony, in its pure variety, is translucent milky white in color. Chalcedony, like other gem materials, gets its different colors from minute traces of other elements, which stain it. For example, carnelian (brownish-red/orange) is caused by iron and heat, chrysoprase (yellowish-green) is created by nickel, and gem silica chrysocolla (bluish-green) is colored by copper.

While Fraser and others believe that unknown trace elements cause chalcedony’s blue color, another hypothesis cites “interference of light caused by voids between the individual crystals—also called scattering.” Johnson explains: “Blue chalcedony is composed of compact masses of tiny quartz crystals, and the size of these crystals can vary, as can the amount of spacing between crystals. As a result, properties such as hardness and reaction to light and coloring agents can, and usually will, differ in various specimens or within portions of the same specimen. This is particularly true of blue agate. Blue agate layers can, and usually do, vary in color, texture, and transparency. Due to impurities, there are often brown, gray, white, or colorless layers interspersed with and modifying the color of the blue layers.”

This not only affects color, says Johnson, but also proves why proper selection of rough, along with savvy cutting, is essential to creating a fine gem.

Value

Johnson points out that while there are many similarities between samples from various sources, there are also distinctive, characteristic, differences. “I personally feel very strongly about the need to disclose the origin of these stones in the course of commercial transactions,” Johnson says. “All sources have produced beautiful gems. Some varieties, such as the Ellensburg Blue, found sparsely scattered in vast alluvial gravels, are valued as much for their rarity as for their beauty. A premium is paid for fine gems from this source, and that is as it should be. However, every source of gems is finite. And every beautiful stone, regardless of origin and rarity, is a thing to be treasured.”

Chalcedony can have another trait that’s quite desirable. It can form in botryoidal (grapelike) structures that reveal themselves either internally, called “turtle-backing,” or externally, called “bubble-top.” For Johnson, locating “bubble-tops” in facet-grade material is the ultimate find.

Note for Cutters

Johnson has found that brown or gray layers can influence the color of blue or purple chalcedony. “This can be the thinnest, most transparent, most seemingly inconsequential of layers,” he says. “But the inevitable result is the muddying of the preferred colors. This is the curse of otherwise world-class Mexican nodules and is the bane of the Holly and Indonesian lavenders.”

“Some would say that lavender is closer to the blue end of purple, while violet is the red end of purple,” says Fraser. “I tend to associate lavender with a lighter tint of purple. As for Holly Blue, I would say it is a lavender purple. However, I have always been kind of puzzled on where these vague color differences happen.”

He adds, “Years ago I bought rough called purple chalcedony, similar in color to Holly Blue.” The “lavender” he saw last year ranged from muted grayish purple to deep purple, and “some had a bit of a brownish look.”

It Wouldn’t Be Chalcedony Without Turkey

“The mine area is Eskisehir city, meaning ‘old city,'” says Kadir Korkmaz, spokesperson for ArtIstanbul, manufacturers in Istanbul, Turkey. “Our office and warehouses are in Istanbul and Kadikoy. Kadikoy, also named Chalcedon, is the old ancient trading area. Historical writings say that chalcedony of any color is named for the ancient seaport of Chalcedon, now Kadikoy, Turkey.”

As one would expect, this area has a long history in jewelry. Archaeologists have dug up Babylonian and Assyrian chalcedony cylinder seals dating from 2500 to 500 B.C.