November 2016

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Topaz in matrix (Photo GIA)

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 quartz.”

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.)

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.

 

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.

This untreated 45-carat imperial topaz displays an attractive reddish peach color. (Photo: Constantin Wild, Idar-Oberstein)

Spectacular prize-winning, orangy-red, flame-shaped Imperial Topaz gem. (Photo: Gem courtesy of John Dyer & Co.)

The Württemberg Pink Topaz Tiara

The Württemberg Pink Topaz Tiara features pink topaz stones 

This tiara is part of an extravagant parure which includes, the tiara, two bracelets, a pair of earrings, and a devant de corsage (large brooch).  The set features a series of large and small pink topaz stones, surrounded by diamonds, mounted in gold and silver.

Princess Marie in the Topaz Parure

All of the pieces feature diamonds and striking pink topaz. The topaz stones are believed to be sourced from Russia.
The parure is linked to Princess Marie of Waldeck and Pyrmont (1857-1882), who married Prince William of Württemberg (later King William II) in 1877. Marie died just five years later following complications during the birth of her third child, a stillborn daughter.  Her pink topaz jewels are no longer with the Württemberg family and were last associated with the Faerber Collection.

 

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Gemology 101

Allochromatic: When color is caused by impurity elements or defects in its crystal structure rather than by an element of its basic chemical composition.
Idiochromatic: An idiochromatic gem is one where the color is not due to impurities, but where the coloring element is an essential part of its chemical formula. An example of an idiochromatic gemstone is peridot, because iron is part of its makeup; no iron, no peridot. 
Pleochroic: Pleochroism is when a gemstone shows different colors in different crystal directions. 

Pleochroism in a tourmaline cut with the c-axis parallel to the table, as seen with the unaided eye through the side (left), crown (center), and end (right). (Photos: Wimon Manorotkul and Mia Dixon.)

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October 2016

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october

American Contra Luz Opal from Oregon, Sold by Bonhams Auction House

Opal

Opal is formed in dry areas such as Australia’s semi-desert “outback.” Seasonal rainwater drenches the dry regions and showers soak deep into ancient underground rock, carrying dissolved silica (a compound of silicon and oxygen) downward, forming deposits in cracks between rocks. During dry seasons much of the water evaporates, leaving the silica deposits underground in the cracks and fissures of sedimentary rock.

Depending on the conditions in which it formed, opal may be many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these, black opals are considered the most rare while white and greens are the most common. 

As with their color opals vary in optical density from opaque to semitransparent, and there are two broad classes of opal: precious and common. Precious opal displays play-of-color while common opal does not.

Play-of-color occurs in precious opal is due to the way in which silica is arranged on a sub-microscopic level. Opal is made up of sub-microscopic silica spheres that arranged in a grid-like pattern (think of it like a box of ping pong balls). This arrangement causes light to bend (diffract). As the light bends it breaks apart into spectral colors (all the colors of the rainbow) producing an incredible display of color.  The color that can be seen varies with sphere size. According to GIA "spheres that are approximately 0.1 micron (one ten-millionth of a meter) in diameter produce violet. Spheres about 0.2 microns in size produce red.  Sizes in between produce the remaining rainbow colors".

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Opalized Fossils

OpaliZed freshwater mussell shells 110 million years old

What are Opalized Fossils?

Opal usually forms within fissures in rock layers, but opal can also form in other materials. If a cavity has formed because a bone, shell or pine-cone was buried in the sand or clay that later became the rock, opal may form in these cavities. 
One of the richest sources of opalized fossils is Lightning Ridge in northwestern New South Wales. These fascinating fossils transport us back in time approximately 110 million years! The fossils of dinosaurs, marine reptiles, fish, early mammals, mollusks, and plants give us a window into our planet's history. 

There are two kinds of opalized fossils:

Type 1. In this type the internal details are not preserved. The water and silica solution fills an empty space left by a shell, bone, etc. that has disintegrated away and then hardens to form an opalized cast of the original object. The opal inside doesn’t record any of the creature’s internal structure. Most opalized shell fossils are this type of ‘jelly mold’ fossils. 

Type 2. In this type internal details preserved: If the buried organic material hasn’t rotted away and a silica solution soaks into it, when the silica hardens it may form an opal replica of the internal structure of the object. This happens most often with with wood or bone.

OpaliZed theropod dinosaur tooth. Lightning Ridge, New South Wales.

OpaliZed Fossil Wood from Queensland Australia

The Virgin Rainbow

THOUGH superficially Belemnites resembled squid, they are distinct from modern squid for several reasons. they possess hard internal shells/skeletons composed of calcium carbonate and also lacked the pair of specialized hunting tentacles POSSESSED by modern cuttlefish and squid. belemnites instead hunted with ten arms covered in tiny hooks. (Artist's depiction of a belemnite school)

The Virgin Rainbow, it was discovered in the opal fields of Coober Pedy by opal miner John Dunstan in 2003. 
It's actually an opalized fossil, from an extinct cephalopod called belemnitida that existed during the Mesozoic era. During that time, much of South Australia was under a vast sea that was filled with prehistoric aquatic life. When these creatures died they sank to the bottom of the sea and were buried by sediment.

Over the millennia the sea eventually dried up and the land turned into a desert. The acidity levels in the shallow top layer of the sandstone increased causing the release of silica from weathering sandstone. Groundwater then carried it down to the layer of clay beneath, where bones and pockets left by disintegrated bones lay buried.

Further weathering lowered the acidity levels allowing the silica gel to harden into opals in the pockets and impressions left by decayed animal material to create a replica of the internal structure (see a description of opalized fossil types above).

The famous Australian opal fields of Coober Pedy are located in this prehistoric sea region. No other environment in the world is known to have undergone this same process, which very well may be why over 90 percent of the world's opals come from South Australia.

Artist rendering of a Plesiosaur next to the Addyman Plesiosaur

Opalized fossils in this region are not uncommon. The South Australian Museum is home to a spectacular (almost complete) opalised skeleton of a six-metre (20-foot) plesiosaur known as the Addyman Plesiosaur, although you have to look closely to see its opalescent sheen. This is not the case with the Virgin Rainbow.

The Virgin Rainbow opaliZed fossil of an extinct cephalopod called belemnitida that existed during the Mesozoic era.

"You'll never see another piece like that one, it's so special. That opal actually glows in the dark -- the darker the light, the more colour comes out of it, it's unbelievable," said Dunstan.

"I've done a lot of cutting and polishing [of opals], I've been doing it for 50 years, but when you compare it to the other pieces that claim to be the best ever, this one just killed it." 

The Virgin Rainbow is considered to be the finest opal ever unearthed and is worth more than $1 million. (In case you were wondering the Virgin Rainbow isn't even the most valuable opal in the world! A massive, 3.45-kilogram (7.6-pound) stone named the Olympic Australis opal, excavated in the Coober Pedy in 1956 gets that honor. In 2005, the Olympic Australis was valued at $2.5 million.)

Both the Addyman Plesiosaur and the Virgin Rainbow are currently on display among a dazzling collection of opals at the South Australia Museum in an exhibition, called "Opals". The exhibition began in September 25, 2015 and will run until February 14, 2016. 

"From jewellery to fossils to specimens embedded in rock, visitors will be treated to a spectacle of unmatched colour and beauty. This is an exhibition literally millions of years in the making because these opals were formed back when dinosaurs walked the earth and central Australia was an inland sea," - Museum Director Brian Oldman.

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Gemology 101

Aboriginal Origins of Opal

"The Path of Enlightenment" necklace contains 180 magnificent opals from Lightning Ridge, Australia, a famous opal producing area. - Courtesy Cody Opal

We Came From the Land  
This aboriginal story teaches how areas around the Flinders Ranges were created and the origins of opal. This is a Wirangu story from near Ceduna on the west coast of South Australia as told by M. Miller and W.J. Miller.

A long long time ago, a huge meteorite hurtled towards the earth from the northward sky, and smashed into the ground near Eucla. Because it was so big, a dent appeared in the crust of the earth and the meteorite bounced high into the air and out into the Great Australian Bight where it landed with an enormous sizzling splash. It was hot from its trip through space so it gave off a great deal of steam and gas as it sank through the waves. But this was no ordinary meteorite. It fact, it was the spirit Tjugud.
In the deep water near by, the spirit woman Tjuguda lay asleep. All the noise around her woke her up and she was very angry. She bellowed and the elements roared with her. The wind blew, the rain pelted from the sky and the dust swirled.
From the joining of the two spirits, the Tjugud and Tjuguda, a man was born, but he was no ordinary man, he was of enormous proportions. He rose from the deep water of the Bight to swim through the maze of limestone caves which run through the earth and into the sea. Then, he emerged from the ground through the cave of the Nullabor.
This was the birth of the Wirangu man, a coastal dweller. Wirangu walked towards the east, taking huge steps in keeping with the stature of the man. Each time he stepped, the ground shook and a dent appeared in the earth. These would later fill with water and are the rock holes which can still be seen today. You can clearly trace the journey of this man.
When he reached Coober Pedy, he was very hungry so he found some food and then lit a fire. The fire he built was so fierce it burned with an enormous amount of heat. A lot of water from the body of the man dropped into the ground and was captured by the stones which held a lot of water anyway. The beautiful colours from the raging fire went down into these stones, changing the water into a magnificent display of color. This is the colour of the opal and can be found in the stones still.

(Education Department of South Australia 1992: 32-33)

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Sapphires are a color variety of corundum, a crystalline form of aluminium oxide. Corundum is one of the hardest minerals, rating 9 on the Mohs scale. Corundum gems of most colors are called sapphires, except for red which is called Ruby. Multi-color sapphire earrings in 18kt yellow gold. Available from Valentin Magro

Montana Sapphire and Diamond brooch by JAR

Montana's Sapphires

The official nickname for Montana is "The Treasure State" because of its rich mineral reserves. The mountains of Montana have yielded gold and silver since the first substantial deposits were discovered in the mid 1800's. Montana is also home to one of the most valuable gemstones that can be found in the United States of America: sapphires. 

Montana Sapphires. Photo courtesy of Georgetown Lake

Sapphires were first discovered in Montana in 1865, in alluvium (a deposit of clay, silt, sand, and gravel left by flowing streams in a river valley) along the Missouri River by Ed "Sapphire" Collins. Collins sent the sapphires to Tiffany's in New York City, and to Amsterdam for evaluation. These stones however, had poor color and of overall low quality and little notice to them beyond giving Montana sapphires a poor reputation.

Corundum was later found at Dry Cottonwood Creek near Butte in 1889, Rock Creek near Philipsburg in 1892, and Quartz Gulch near Bozeman in 1894. Sapphires from these three sites are routinely heat-treated to enhance color. Millions of carats of sapphires have been mined from the Missouri River deposits, but since the 1990’s there has been little commercial activity. This is because of the high cost of recovery as well as environmental concerns. Production at Dry Cottonwood Creek has been sporadic and low-yielding. Other than Yogo, the majority of the sapphire producing areas Montana sapphire mines produce few blue sapphires and non-blue sapphires have low profit margins. The Rock Creek area (also known as Gem Mountain) is the most productive site in Montana (even moreso than the Yogo Gulch area). Rock Creek has produced over 190,000,000 carats of sapphires since 1906. 

Even with the mining difficulties and expenses, more gem-quality sapphires are produced in Montana than anywhere else in North America. The term "Yogo sapphire" is the preferred wording for gems found in the Yogo Gulch, whereas "Montana sapphire" generally refers to gems found in other Montana locations. The gemstones have made such an impact on the state that in 1969, the sapphire and agate were jointly declared Montana's two official state gemstones. The stones have also  influenced the naming of features including the mountains near Rock Creek Montana which are known as the Sapphire Mountains.

Yogo Sapphires

Yogo sapphires are sapphires that are only in Yogo Gulch, part of the Little Belt Mountains in Judith Basin County, Montana, United States. Yogo sapphires are typically a cornflower blue color which is attributed to trace amounts of iron and titanium. About two percent of Yogos are purple, due to trace amounts of chromium. A very small number of rubies have also been found at Yogo Gulch. 

0.43 carat, cornflower blue Yogo sapphire from Yogo Gulch, Montana. Photo by Pumpkinsky

0.37 carat, purple Yogo sapphire from Yogo Gulch, Montana. PHOTO BY PUMPKINSKY

Yogos are considered unique in that they are usually free of cavities and inclusions, have high uniform clarity, lack color zoning, and do not require heat treatment due to their uniformity. Yogo sapphires tend to be small, but very expensive. The roughs tend to be small and flat, making faceted Yogo sapphires heavier than 2 carats exceptionally rare. Approximately 10 percent of faceted stones from the Yogo area are over 1 carat. The largest recorded Yogo rough was found in 1910 and weighed 19 carats. The stone was faceted into an 8-carat gemstone. The largest faceted Yogo is 10.2-carat. The rarity of large rough Yogo sapphires means that prices for the gemstones begin rising sharply over the 0.5 carat mark. 

The rarity of Yogo sapphires is also due to difficult mining conditions. Yogo sapphires were first discovered in alluvial (river streambed) deposits during gold mining operations downstream from the Yogo dike. Later the source was traced to igneous bedrock. Three other Montana locations also have alluvial sapphires (upper Missouri River, Rock Creek, and Dry Cottonwood Creek). The Yogo sapphires that are found in igneous rock are more difficult to acquire since the only way to extract them is through the difficult process of hard rock mining. This difficulty together with American labor costs makes their extraction fairly expensive. Because of the sporadic mining activity over the years, it is estimated that at least 28,000,000 carats of sapphires are still in the ground. 

Location of the Yogo mine area from a 1902 USGS topographic map

Yogo sapphires were not initially recognized or valued. Even so, Yogo sapphire mining has turned out to be very valuable. 

Yogo Gulch lies in a region originally inhabited by the Piegan Blackfeet people. Gold was first discovered at Yogo Creek in 1866, but the small numbers of early prospectors were driven off by local Native peoples. During the 1878 Gold Rush in 1878, approximately one thousand miners descended on Yogo Creek looking for gold. Miners noted that "Blue pebbles" along with small quantities of gold that were found. The mining camp at Yogo City followed the pattern of many gold towns of the era flourishing for a brief three years, and then the population dwindled to only a handful of people.
Yogo City was briefly known as Hoover City, named for Jake Hoover. who is credited as the discoverer of the Yogo Sapphires in 1894. Sapphire mining began in 1895 after Hoover sent a cigar box of “blue pebbles” he had collected to an assay office. The assay office then sent them via regular, uninsured mail to Tiffany's in New York City for appraisal by Dr. George Frederick Kunz, who pronounced them "the finest precious gemstones ever found in the United States". Tiffany's sent Hoover a check for $3,750 (approximately $106,700 which would be approximately in 2016) and a letter describing the blue pebbles as "sapphires of unusual quality".

Hoover purchased the original mother lode from a sheepherder, later selling it to other investors. This became the "English Mine", which operated and was profitable from 1899 until the 1920s. A second less profitable operation called the "American Mine" owned by a series of investors operated in the western section of the Yogo dike. The “American Mine was eventually bought out by the syndicate that owned the English Mine. In 1984, a third set of claims, known as the Vortex mine, opened.

Sapphire mine of Yogo District, Montana. Face of dike in open cuttings 1897. Photo from Geography of the Little Belt Mountains, Montana, by Walter Harvey Weed and Louise Valentine Pirsson, 1900, United States Geological Survey, Washington DC.

Sapphire mine of Yogo District, Montana. Mine shaft 1897. Photo from Geography of the Little Belt Mountains, Montana, by Walter Harvey Weed and Louise Valentine Pirsson, 1900, United States Geological Survey, Washington DC.

In the early 1980s, Intergem Limited, which controlled most of the Yogo sapphire mining at the time, marketed Yogo sapphires as the world's only guaranteed "untreated" sapphire. This innocent sounding marketing claim exposed the general public to a not talked about common practice that existed in the sapphire world, the enhancement of a sapphire’s color through heat treatment. It was estimated that approximately 90 - 95 percent of all the world's sapphires were heat-treated to enhance their natural color. Intergem eventually went out of business, but the stones continued to be sold. In 1994 Citibank (who had obtained a large stock of Yogos as a result of Intergem's collapse) sold a collection of the sapphires, that had been in a vault for nearly a decade, to a Montana jeweler. Today the major mines are inactive and any mining is largely done by hobby miners or rockhounds in the area.

Yogo Sapphires that are part of the Smithsonian Collection

Jewelry containing Yogos was given to First Ladies Florence Harding and Bess Truman. Montana sapphires, including Yogo sapphires, can be seen in various museum collections.

Detail of the Tiffany Iris Brooch by Paulding Farnham circa 1900, currently held by the Walters Art Museum

Sketch for the Tiffany Iris Brooch by Paulding Farnham. Farnham served as the chief designer and director of the jewelry division of Tiffany & Co. from 1893 until 1907 when he was replaced by Louis Comfort Tiffany. 

The Conchita Butterfly Brooch

The Conchita Montana Sapphire Brooch. The Butterfly can be worn as a brooch or as a pendant.  It has boxes attached so that it can be incorporated into an elaborate neckpiece or strung with beads as well.

This magnificent butterfly brooch is made up of Montana Sapphires. The brooch demonstrates their wonderful range of color and a Yogo sapphire is prominently featured on the head of the butterfly.  The brooch was a collaboration by designer Paula Crevoshay and gem dealer Robert Kane of Fine Gems International. Fine Gems International has the world’s largest stock of Montana sapphire—thanks to its 2001 acquisition of the entire inventory of American Gem Corporation, mined at Rock Creek, Montana’s richest alluvial sapphire deposit, in the mid-1990's. Blue to green-blue are the most predominant colors in this large selection of sapphire. It was gifted to the Smithsonian Museum in 2007 and is part of the National Gem Collection at the Smithsonian.  The piece includes 333 sapphires weighing 27.97 carats and 98.48 grams of 18K gold.

An excerpt from Pauala Crevoshay talking about the Conchita Butterfly brooch's creation:

A year ago a Smithsonian spokesperson approached me asking if I would be willing to take an amazing collection of Montana sapphires that were so generously being bestowed to the Museum by Robert Kane of Fine Gems International and create a finished jewel for our nation’s Gem and Mineral collection so the many small stones could be preserved and beautifully displayed.
Without a moments hesitation I answered, “I would be honored.” The process unfolded like a flower with all its many stages.
First, there was the question of what these delicious, highly refractive sapphires would wish to become. I felt our National gem and mineral collection should have a marvelous image to symbolize our nation’s immeasurable natural beauty that the sapphires from Montana represent.   As I pondered the range of colors of Montana sapphires with their many primary and secondary hues, I decided I would like to honor my mother’s amazing spirit and her love of the butterfly. As a child living in the Deep South I would catch Monarch butterflies every season just to see their magnificence a little more closely (and then of course let them go).  My mother had raised me to believe that the butterfly symbolized the Holy Spirit, Resurrection and Creation itself.
I have named the butterfly “Conchita” as my mother has left the physical plane and her deep connection with nature, spirit and freedom touches all that I am or do.
The artistic vision and creativity that flows abundantly through me always seeks an anchor to balance that flow and channel it into the finished product. That is where the academic and scientific brilliance of Robert Kane enters. This blessed spirit focused the selection and fine tuning of the gemstones so that each one set was perfectly cut to classical proportions and were perfectly clean under high magnification.  His uncompromising integrity and commitment blending with my creativity and free spirited truth produced a jewel that will become part of our great nation’s heritage and a source of delight and learning for generations to come.
Paula Crevoshay
February, 2007

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Gemology 101: Two Jewelry Terms

Collet Setiing: A Collet setting (also called a bezel setting) is a ring or rim of metal, designed to encircle the girdle of a gemstone. The upper edge of the collet is then pressed over onto the stone to secure the gem in place. Collets may be plain or decoratively enhanced with carving, piercing or millegraining.

Navette: Navette is French for "little boat", because it resembles the hull of a sailboat. It is a term used to describe a gemstone or jewelry piece that is oval with a point at both ends. The alternate term for gemstones cut in this shape is marquise-cut. 

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