Bohemian Garnets

This Brooch Dates From the Third Quarter of the 19th Century. (Photo Courtesy the National Czech & Slovak Museum & Library)

“Bohemian garnets” are garnets mined in an area once known as Bohemia (it often refers to the entire Czech territory, including Moravia and Czech Silesia). They are the variety of garnet called pyrope (from the Greek words pyr for “fire” and ops for “eye”). Those found in Central Bohemia (in the north of the Czech Republic) are considered to be of the highest quality. 
The Bohemian garnet has been mined for over 600 years mostly dug at the mines of Meronitz, and chiefly in the northwestern part of the Czech Republic. The garnets are found in a gravel or conglomerate, resulting from the decomposition of a serpentine. Sometimes, however, they are found in the matrix. When this happens they are often associated with a brown opal. Most of the good quality the stones are small with those as large as approximately 1/4 inch and above being reported rarely. By the 19th century it was determined that the elements creating the intense red color in pyrope were Chromium and Manganese. The color ranges from fiery-red to ruby-red. The Bohemian garnet also possesses excellent clarity, transparency, and has a high refraction of light. This means that the stone has a remarkable sparkle and what has been described as an "inner glow".

The stone gained popularity in Europe in the 18th and 19th century also becoming a favorite of the Victorians. Traditional Bohemian design placed it's emphasis on the arrangement of the garnets, taking precedence over the metal chosen for a piece of jewelry. George Frederick Kunz cites in his book Rings for the Finger Garnet that rings were generally made of faceted, rose or cabochon cut Garnets in 14 or 18 kt gold. By the late 19th century larger Pyropes were typically brilliant-cut, resulting in very bright (red) stones, whereas the very small stones were usually rose-cut. 

View fullsize

This Art Nouveau Style First Appeared in Individual Creations of Designers Rather Than in Industrial Mass Production. (Photo Courtesy The National Czech & Slovak Museum & Library)

An Example of the Mass Produced Items Typical of the Bohemian Garnet. (Photo Courtesy The National Czech & Slovak Museum & Library)

The introduction of larger scale manufacturing of garnet jewelry created mass-produced machine pressed metal settings and garnets of inferior quality. The majority of readily available "Bohemian Garnet" antique jewelry falls into this mass production category. While these pieces are beautiful in their own right, it should be noted that like any piece of jewelry rarity and individuality are valued much more highly. 

View fullsize

Antique Pyrope Hairpin From the Smithsonian

Sardonyx

A Roman sardonyx cameo of Minerva from the Julio-Claudian period circa 1st century AD. Sold by Christie’s.

The second of August’s birthstones is sardonyx. This is a very underrated stone in my opinion. 
Sardonyx is a variety of Agate with parallel bands of white (or black) contrasting with the brownish-red (sard) body color. Because of its layered nature sardonyx stones have been and are ideal mediums for cameo, intaglio and relief carving.
Agate in turn is a variety of chalcedony which is a variety of quartz. It has a mohs hardness of 6.5-7. 
 

Kathleen Marino MA, GG, AJP, NAJA

Peridot

The largest cut peridot olivine is a 310 carat specimen in the Smithsonian Museum in Washington, D.C. Photo courtesy of the Smithsonian Museum

Welcome to August and a very happy birthday to all of the August babies out there! You have two great birthstones peridot and sardonyx. Here is a little about peridot.
Peridot is gem-quality olivine. Olivine is a silicate mineral and has a mohs hardness of 6.5-7. This is almost smacked dab in the middle of this hardness scale so don’t be afraid to wear it in any type of jewelry. 
Olivine in general is a very abundant mineral, but gem quality peridot is rather rare. Peridot olivine is mined in Arkansas, Arizona on the San Carlos Reservation, Hawaii, Nevada, and New Mexico at Kilbourne Hole, in the US; and in Australia, Brazil, China, Egypt, Kenya, Mexico, Myanmar (Burma), Norway, Pakistan, Saudi Arabia, South Africa, Sri Lanka, and Tanzania.
Peridot ranges in color from yellow, to yellow-green, olive-green, to brownish, sometimes a lime-green, to emerald-ish hue.

Photo courtesy of Bonhams

This late 19th century peridot necklace, was sold by Bonhams Auction House in 2011.

Zircon

We are marking the end of the year with another of December’s birthstones: Zircon

In the past when many people heard the word “zircon” (a naturally occurring gemstone) they immediately jumped to something more familiar, “cubic zirconia” (a man-made diamond simulant). In the current market, consumers have become more savvy in understanding that there is a difference; however, even though many people may have heard of zircon very few have ever encountered it.

Red Zircon Crystal, Kunar Prov., Afghanistan Photo courtesy of http://www.marinmineral.com/

Some gemologists classify zircons into three types—high, intermediate, and low.
The majority of zircon is generally of the low and intermediate variety. This is directly related to the chemical makeup of zircon. Zircon a zirconium silicate containing trace amounts of the radioactive minerals hafnium, uranium and thorium. Over time, these radioactive components can break down and destroy the internal lattice of the crystal (over tens of thousands of years). This leaves the zircon with an amorphous structure that has a pithy appearance. “Intermediate” zircon is also exposed to the damaging effects of radiation but to a lesser extent than low zircon.
Virtually all zircon that is used in jewelry is of the “high” variety. Zircon that is of the “high” variety is geologically “young” and virtually unaffected by radioactivity. These high zircons have full crystal structures and as a result, they have the normal physical and optical properties which are compatible with faceting. "High" zircon can also be heat treated to create colorless, blue or golden stones.

The many colors of Zircon Photo courtesy of GIA

The stone comes in a beautiful array of colors including warm browns and lovely shades of cinnamon, sherry, yellows, oranges, and reds. The most well known of the colors are the vibrant bright blues (which may be enhanced by heat treatment). It has been estimated that approximately 80% of all zircons sold are blue, and usually command a slightly higher price. Blue topaz is often offered as a less expensive alternative.
In the early 1900s zircon was often used as a diamond simulant. Due to its doubly refractive nature, zircon displays a high amount of “fire”, even greater than that of diamond, adding to the appeal of the stone. As new technology emerged it was replaced with more convincing look-alikes including many imitations, and it’s name still brings to mind the word “imitation today”. This is sad because zircon is a beautiful stone with a wide range of colors and its own charming history and lore.  

Zircon Ring ca.1850 Photo Courtesy of the Victoria and Albert Museum

"Many scholars think the stone’s name comes from the Arabic word zarkun, meaning 'cinnabar' or 'vermilion.' Others believe the source is the Persian word zargun, or 'gold colored.'  Considering zircon’s color range, either derivation seems possible.” (GIA).
In the Middle Ages, zircon was believed to aid in sleep, keep away evil spirits, and promote riches, honor, and wisdom. 

Cat's-eye Zircon Photo courtesy of GIA

 
Blue zircon especially was a favorite of the Victorian Age. Zircons are usually relatively free of inclusions, but many untreated zircons may have a cloudy or smoky appearance. If it’s very noticeable, this can negatively affect price. In Victorian times, this smokiness made zircon a popular gem for mourning jewelry.
The majority of modern zircon that is used in jewelry will not have eye visible (visible to the naked eye) inclusions.  Long, parallel, visible inclusions can make the stone desirable when it is cut into a cabochon because it may create the cat’s-eye effect.

It’s a challenge to cut zircon because the gem is brittle. Cutters usually fashion zircon in the brilliant style to take advantage of its luster and fire. In the past, cutters developed a modification of the brilliant cut, known as the “zircon cut,” which uses eight extra facets around the pavilion (the gem's lower portion). In modern times this is rarely seen, as the added labor required makes it not cost effective. Zircon can also be found in step cuts (rows of parallel facets), and mixed cuts (a combination of brilliant and step-cuts). 

The fact that the gemstone has been passed over for so long is an absolute shame. Gemologist and author/researcher George Kunz (a famed gemstone buyer for Tiffany & Company) attempted to rename the stone “starlite”, owing to zircon’s high fire, to promote the gemstone. However, the name failed to catch on and over time the stone seemed to fall by the wayside. There may be a potential upside to the relative obscurity of zircon though. Analysts in the gem industry have stated that zircon has yet to reach its full potential in value, and it will only appreciate in value so it may be an excellent time to branch out and embrace the beauty of zircon.

The final word:
Zircon is Not Cubic Zirconia! Zircon is a naturally occurring mineral found in the earth. Cubic zirconia is a man-made diamond simulant. They have both been used in place of diamonds, though cubic zirconia is used much more commonly than zircon in modern times. The differences are easy for a trained gemologist to spot. When in doubt ask an independent gemologist.

Basic Information:
Formula: ZrSO4, May contain minor U, Th, Pb, Hf, Y/REE, P and others.
Crystal Systems: Tetragonal
Hardness: 7-1/2
Color: Yellow, Clear, Blue, Pink, Brown...etc
Lustre: Adamantine, Vitreous, Greasy
Mineral Group: Zircon
Major sources: Major sources of zircon are the Chanthaburi area of Thailand, the Palin area of Cambodia, and the southern part of Vietnam. 
Misc: Eye visible, strong double refractivity. This causes high fire that is more noticeable in light colored stones but may be seen even in darker stones. 

Quartz Varieties

Let's talk about something that drives me nuts. Amethyst is a purple variety of quartz. It is ONLY SHADES OF PURPLE by definition. "Green amethyst" does not exist and we need to start demanding that the proper names be used.
That being said let's run through the colors and the quartz varieties:

Green quartz = prasiolite 
purple quartz = amethyst 
purple and golden quartz = bi-color quartz, ametrine,
pink quartz = pink/rose quartz
yellow quartz = citrine 
brown quartz = smoky quartz 
black quartz = black quartz
clear quartz = rock crystal quartz or clear quartz
blue quartz = blue quartz to varieties of greenish blue, and a bright clear pink (almost always synthetic and easily identified by gemologists) 

Synthetic Quartz forms in tube shapes due to the machines used to grow them  photo courtesy of WKSU news

Also a quick word on treated and synthetic quartz. Much of the quartz (colored varieties) you see on the market are heat treated. Heat treatment can enhance or alter the color of quartz. Treatment is difficult to detect, but it is almost always assumed. 
Over the years I have also seen a lot of synthetic quartz. It is often times cut into very large stones. There are telltale indicators of synthetic quartz (that are related to the way in which it is grown) that an experienced gemologist can quickly identify.  
Synthetic quartz is just as expensive as natural quartz varieties. The is mainly due to the fact that the majority of consumers cannot tell the difference. 
As an aside, the market for synthetic quartz has always been strange to me since quartz is one of the most plentiful gemstone materials available.

How quartz is synthetic grown     photo courtesty of voguecrystals.com

Kathleen Marino M.A, G.G., AJP, NAJA

Additional photos courtesy of: Gemselect.com, gemcutter.com, dannytherockman.com, wksu news, www.voguecrystals.net,

Turquoise: The Desert Beauty

A turquoise and gold ring which once belonged to Jane Austen Sold by Sothebys

The most traditional birthstone for the month of December is Turquoise and  the zodiacal stone for Sagittarius. Opaque, varied blue colors that has been used for centuries in jewelry and in decorative ornaments.

If cold December gave you birth,
The month of snow and ice and mirth,
Place on your hand a turquoise blue;
Success will bless whate'er you do.

Turquoise is found in various locations around world that all share the same characteristics: dry, arid, barren and possessing acidic, copper-rich ground water. This ground water creeps downward it reacts with other minerals. The product of this process is the compound of hydrated copper and aluminium phosphate known as turquoise.

The deposits of turquoise usually form in iron-rich limonite or sandstone. The remnants of these host minerals (called the matrix) are what leave the veins or splotches on the turquoise. (Limonite creates the darks brown markings and the sandstone creates tan markings)
The texture of turquoise is a result of both its structure and composition. If you look at turquoise under a microscope you may see that it is actually an aggregate of microscopic crystals that form a solid mass. The closer the crystals are packed, the finer the texture and the less porous the material. Fine textured turquoise has a shiny waxy luster when it is polished, while less dense turquoise results in a duller luster.

Turquoise from Bisbee Arizona

The porosity also affects the stones' durability with the less porous turquoise possessing less toughness. Because of the decreased visual appeal and the lesser amount of durability more porous turquoise is often treated to make it smoother, shinier, and more marketable.

                                                                                                                                                                                  Most people will be familiar with vein like black matrix running through the vibrant blues or greens; however, the most expensive and prized turquoise has no matrix showing. The second most valuable is a thin web like matrix that is evenly distributed throughout the stone.This really is personal preference, and some turquoise lovers may find imperfections part of the charm.

Turquoise is very soft, ranking a 5-6 on the Mohs hardness scale. This makes the stone ideal for carving and artists throughout history in Europe, Asia, the Middle East and  the Americas have utilized it as a medium for both jewelry and art objects.

Turquoise has a long and varied history (that continues to this day) of being used as talismans, amulets, or religious artifacts as it has been attributed to have special power and meaning to various cultures. The ancient Egyptians, Meso-Americans, Native Americans and Tibetans have believed in the special powers of turquoise for centuries. Some believed that turquoise can protect its wearer from harm, others thought that it brought good luck or longevity, and some uses and meaning have been lost to history.

                  Egyptian middle Kingdom faiance hippo
                                       The MET Museum

The high value placed on fine turquoise caused many imitations to be made. The first of which dates back to ancient Egypt: a glazed earthenware material called faience. Later glass, and enamel were used. In modern times plastic, porcelain, composites of minerals were used. In 1972 the closest “synthetic” turquoise was produced by Pierre Gilson. I put synthetic in quotes since it is actually called a simulant owing to its chemical composition differing from actual turquoise due to a bonding agent. The simulated turquoise is available in both fine and spiderwebbed varieties.

The most common natural stone imitators of turquoise that might be encountered are dyed howlite and magnesite. These stones are both white in their natural state and contain black veining.

All of these imitators are fairly easy to identify by a  trained gemologist and many can be identified by the general consumer as well.

Basics:
Chemical Formula: CuAl6(PO4)4(OH)8•4H2O Copper containing basic aluminium phosphate
Hardness: 5 to 6 on the Mohs scale
Formation:Turquoise occurs as botyroidal (grape-like) masses or nodules in fissures.
Found in: Currently the finest quality turquoise is found in Northeast Iran. Major turquoise deposits are also found in Afghanistan, Argentina, Australia, Brazil, China, Israel, Mexico, Tanzania and the USA.