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

Nicholas Varnay and K2

Nicholas Varney Blue Moonstone and Diamond Earrings: Surrounded by K2, 48 carats Blue Moonstone, 0.60 carats Diamonds. 18K yellow Gold.

A view of K2, also known as Mount Godwin Austen, in the morning sun. With a summit elevation of 8,611 meters, K2 is the second-highest mountain in the world after Mount Everest (8,848 meters), and ahead of Kangchenjunga (8,586 meters). Image © iStockphoto and PatrickPoendl.

One reason I love jewelry by Nicholas Varnay is that he isn't afraid of playing with "unconventional" stones.  One of the most interesting is K2 Granite,” also known as “K2 Jasper.”

What is K2 Granite? 

"K2 Granite," also known as "K2 Jasper," is an extremely interesting and actually slightly controversial rock and lapidary material that comes from Pakistan.

The mineral is a bright white granite that contains beautifully contrasting orbs of bright blue azurite. The azurite orbs can range from a few millimeters up to about two centimeters in diameter that can look like bright blue splashes on a rough pieces. 
K2 Jasper is the most commonly used name for marketing this material, but it is definitely not jasper. If you examine the rock closely you can see that the splotches are actually spherical. You will also see see cleavage faces of feldspar minerals and black flakes of biotite. 

The white granite is fine-grained: composed of quartz, white feldspars, and biotite. 
The azurite is a secondary material that clearly formed after all of the other minerals in the granite had solidified from the parent melt. This can be seen clearly during an examination of the azurite spheres. They are present along the mineral grain boundaries, within tiny fractures, and as a “dye” penetrating the feldspar grains.

I mentioned that this stone has been slightly controversial. When this mineral first appeared on the market the lapidary world did not believe that the blue splotches could be azurite (and to some extent this is still the case). This is because white granite and azurite rarely occur together. For many this is the first time that they have seen the two materials in such close association. 

The Controversy

For the last 3 or so years experienced mineralogists, people from Pakistan who have directly obtained K2 fron it's source, and lapidarists who have worked with K2 cutting cabochons, have had long discussions about the material; sharing observations, photomicrographs, chemical analyses, and x-ray diffraction data trying to learn more about the intrusive mineral, arriving at the conclusion that it is indeed azurite.  Some specimens were also found to have small areas that are stained green with malachite! The science of geology continues to evolve and astound! 

A piece of dry K2 Granite. A wet surface would increase the intensity of the blue azurite orbs. This piece is approximately 10 centimeters across, and the largest azurite orbs are about 1 centimeter across.

An oval cabochon cut from K2 Granite with several bright blue azurite stains. Within each stain you can see the texture of the granite and grains of black biotite. These indicate that the stain formed after the granite solidified from its parent melt. This cabochon is about 20 x 30 millimeters in size.

Where Is K2 Found? 

As stated earlier K2 granite is named after a mountain in the Karakoram Range near the border between Pakistan and China. K2, also known as "Mount Godwin Austen," is the second highest mountain in the world. The azurite granite is found in colluvium near the base of the mountain, in a very remote area visited by very few people. 

So What About Using it in Jewelry?

K2 granite cuts, tumbles, and polishes wonderfully. Due to its high feldspar content, it can be easily cut with a lapidary saw and shapes quickly on a diamond wheel. Azurite has a Mohs hardness of 3.5 to 4, however because the azurite is more of a stain within the mother mineral, the dots have the same cutting and polishing properties as the surrounding white granite. 

As to the durability in jewelry The feldspar minerals in K2 have a hardness of about 6 on the Mohs scale, therefor they can be be scratched or show signs of wear over time if subjected to extensive use, "hard wear", or impact. K2 is therefore not a good stone for mounting in a ring or bracelet, but it is a sunning (and appropriately safe) addition to the earring that inspired this article. 

Kathleen Marino M.A, G.G., AJP, NAJA

A big thanks to geology.com for their extensive research and information on the subject. Another website to visit for more information on the mineralogical makeup of K2 or other minerals is mindat.org

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.