The Colorful World of Topaz

I have always thought it was a shame that the general public has been forced into the misconception that topaz is merely and inexpensive blue gem. Incidentally the blue color is hardly ever natural: It’s almost always caused by treatment. Topaz has a far broader and more colorful story to tell gemstone lovers. 

Topaz is allochromatic. This means that the color you see is caused by an elemental impurity or defect in its crystal structure rather than by an element of its basic chemical composition. For example, the presence of the element chromium causes natural pink, red, and violet-to-purple colors in topaz. Imperfections at the atomic level in topaz crystal structure can cause yellow, brown, and blue color. Brown is a common topaz color, and the gem is sometimes mistakenly called “smoky quart

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THE 97.45-CARAT BLAZE IMPERIAL TOPAZ IS IN THE COLLECTION OF THE FIELD MUSEUM OF NATURAL HISTORY. - (PHOTO: "GEMS AND GEMSTONES: TIMELESS NATURAL BEAUTY OF THE MINERAL WORLD" BY GRANDE & AUGUSTYN, U OF CHICAGO PRESS.)

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Topaz actually has an exceptionally wide color range that, besides brown, includes various tones and saturations of blue, green, yellow, orange, red, pink, and purple. Colorless topaz is plentiful, and (as was mentioned earlier) is often treated to give it a blue color.
The color varieties are often identified simply by hue name—blue topaz, pink topaz, and so forth—but there are also a couple of special trade names. Imperial topaz is a medium reddish orange to orange-red. This is one of the gem’s most expensive colors. Sherry topaz—named after the sherry wine—is a yellowish brown or brownish yellow to orange. You may hear stones in this color range are referred to as "precious topaz". This term is used to distinguish them from less expensive citrine (yellow quartz) and smoky quartz.

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TOPAZ CRYSTALS ARE TYPICALLY ELONGATED, WITH GROOVES PARALLEL TO THEIR LENGTHS. FOR THIS REASON, THEY'RE COMMONLY CUT INTO LONG OVAL OR PEAR SHAPES. THESE CRYSTALS SHOW ORANGE, PINK, AND BROWN COLORS. - ERIC WELCH/GIA

What is Imperial Topaz?

Red is one of the most prized and rare topaz colors. Red represents less than one-half of 1 percent of facet-grade material found. The color known in the gem the trade as "imperial topaz" is even more highly prized and rare. They color is a bit elusive and subjective; however, many dealers insist that a stone must show a reddish pleochroic color to be called imperial topaz. The reddish pleochroic color often appears at the ends of fashioned gems—like pears and ovals—that have an otherwise yellow-to-orange bodycolor. This look is illustrated in the images below. 
The name for "imperial topaz" originated in nineteenth-century Russia. At the time, the Ural Mountains were topaz’s leading source, and the pink gemstone mined there was named to honor the Russian czar. Ownership of the gem was restricted to the royal family.

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THIS UNTREATED 45-CARAT IMPERIAL TOPAZ DISPLAYS AN ATTRACTIVE REDDISH PEACH COLOR. (PHOTO: CONSTANTIN WILD, IDAR-OBERSTEIN)

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SPECTACULAR PRIZE-WINNING, ORANGY-RED, FLAME-SHAPED IMPERIAL TOPAZ GEM. (PHOTO: GEM COURTESY OF JOHN DYER & CO.)

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.