All posts by Houston Wade

Geologist, Geographer, and Astrophysicist. Master of all he bothers to learn.

The Rare Gem Series: Demantoid Garnet

Demantoid?  That’s kind of a satanic sounding name.  The guy who named that stone must have been color blind because they’re green, not red.  Oh well, the Russians named it and used the Dutch word for diamond, “demant”, and the Greek word for alike, “eidos” and mated them together to get “demantoid”.  Discovered on the banks of the Bobrovka river in the central Western Ural Mountains in 1868 the stone quickly became popular among Russia’s elite due to its high indices of refraction and superior color dispersion to that of even diamonds.

Jeffrey Mine Specimen
A rich specimen of demantoid in wollastonite from the Jeffrey Asbestos Mine in Quebec, Canada (minfind.com)

Demantoids are the green version of andradite garnets, a calcium and iron rich silicate mineral.  Garnets are defined in a weird way; they are called “solid solutions”, meaning that the stones will always have a the structure of (SiO4)3 contained with in it, but will be bundled with a different series of atoms to form the particular molecule of the different garnets.  In the case of Demantoids, the molecule looks like this: Ca3Fe2(siO4)3.  I know it is a bit technical, but bear with me.

The Urals are a mountain range born of collision.  They form the seam where the continents of Europe and Asia bonded and made the super continent of Eurasia.  When two continents collide everything gets all orogenous.  As the two massive hunks of Earth merge they have two options: 1) if they are of different densities the denser of the two will subduct (like what happens off the coast of Washington and Oregon between the dense Juan de Fuca Plate and the lighter North American Plate; or 2) if the are the same density (like two chunks of continent) they collide and start to push up as they attempt to override the other equally-matched mass of rock.  We can see this happening today in the Himalayas where the Indian Sub Continent has slammed into South Asia.

The big collision that formed the Urals was about 250-300 million years ago making these mountains among the oldest on the planet.  At one time, when they were a young whipper-snapper, the Urals may have approached 30,000ft in altitude like that of the greenhorn Himalayas.  Time, combined with weather, has reduced the Urals to but a 1,500 mile ridge of hills today ranging from 1,100ft to about 6,000ft at its highest.

When Europe and Asia collided and formed the Urals a lot of rock cooking happened.  When  continents collide and form a mountain range, a bunch of earth is uplifted and piled upon more earth like wrinkles in a bed sheet.  When rocks are buried miles deep they come under great pressure (how long do you think you would last as the bag full of water that is your human form if you had five to twenty miles of rock piled on top of you?), and fantastic temperatures.  Sometimes the temperatures can be in the thousands of degrees!  This heat and pressure metamorphizes rock; essentially there is enough heat and pressure to change the chemical structure of the material, thus creating new minerals in the process.

Metamorphosis is how andradite garnets appear into being.  When the limestones that formed the seafloor between the two colliding continents merged and squished, the added heat and pressure caused mineral leaching.  In Russia, this just happened to occur with some squishing serpentinites (soapstone).  The calcium and iron from these two stones bonded to form the solid solution with the oxygen and silica, that is the basis for all garnets, creating the demantoid.  The special thing about the Russian demantoids is that the serpentinite cased the garnets to form around this stuff called chrysotile which is a form of asbestos.  The thin, long strands of chrysotile make wispy curved inclusions in the stones that look like horsetails.  The demantoids with these inclusions are simply known as horsetail garnets; and they are worth a lot of money.

Microscopic image of a horsetail inclusions in a Russian specimen (Emporia State University, Kansas and the Gemological Institute of America)

From the time demantoids were discovered in 1868, up to the Communist Revolution in 1919, Demantoids were wildly popular.  Even famed jeweler Peter Carl Fabergé (of Fabergé Egg fame) regularly incorporated demantoids into his pieces.  After the revolution jewels were not much of a concern for Soviet population.  Mine production in the Urals started once again in the 1970s when it was realized that outside markets were demanding this extremely rare stone.  Some mining in the Urals carries on today, and rarely some Russian stones can be purchased at auction.

More recent discoveries in Namibia (1996), Madagascar (2009), Italy, Iran, and Afghanistan have come on to the market.  The Jeffrey Mine in Quebec, Canada is producing some of the largest, most beautiful demantoids ever seen.  The Jeffrey is the largest asbestos mine in the world and a big source of contention among Quebecois.

Jeffrey Asbestos Mine Quebec, Canada
The Jeffrey Asbestos Mine is the largest open pit asbestos mine in the Western Hemisphere. It is a fantastic source of mesothelioma and garnets!

Most Demantoids are incredibly small with most gem-quality cut stones being under 1ct.  Stones over 2cts are rare, and stones over 3cts are incredibly rare.  Noosphere Geologic has in its private collection a 5.4ct round-brilliant cut Russian horsetail, as well as a 1.32 oval cut Russian demantoid.  We also have several larger uncut stones in matrix from the Jeffrey Mine, and from Madagascar and Namibia.

The value of demantoids are generally very high.  Eye-clean Russian stones larger than one carat can easily fetch $25,000 to $50,000 per carat, while stones with visible inclusions will get between $1,000 to $5,000 per carat.  The largest eye-clean Russian demantoid is only 8cts and worth upwards of one million dollars.  The largest single stone ever found was a Russian 252.5ct ugly green blob.

5.4ct Russian demantoid
This is a 5.4ct Russian horsetail demantoid specimen (Noosphere Geologic)

In the United States there are several potential locations in the Southeast, Montana, California, and even my home state of Washington where old asbestos mines exist.  If you are going to look, be careful.  Wear masks if recommended, and if you see the long fibrous strands of serpentine (different that serpentinite or soapstone) get out!

The Rare Gem Series: Spinel (The Balas Ruby)

Spinel?  Really, that cheap fake crap that you can get at Forever 21? Rare?  You bet.  To explain why, I have to take you time travelling; going back maybe a thousand years to the domains of some lost civilizations in Central Asia and the Middle East.

Spinel used to not exist; way back when, there were only rubies and sapphires. If it was red, it was a ruby.  If it was a color other than red it was a sapphire.  That was a pretty simple classification, the type of classification that drives my birding roommate up the wall.  To me there are six kinds of birds:  crows, seagulls, not-crows, and not-seagulls, chickens, not-chickens.  I know I’m wrong, but it’s too much fun to watch him pop a vessel when I play the moron.

In the mountains of what is now the border region between Afghanistan and Tajikistan shiny, gemmy red stones were discovered and a very primitive mining began.

The Black Prince Ruby
Queen Elizabeth the Second’s crown is adorned with the Black Prince Ruby, that is actually a spinel.

Who commissioned the mine? When were they opened?  The first known historical reference to these “rubies” was by the Central Asian Divinci of his day, Abū al-Rayhān Muhammad ibn Ahmad al-Bīrūnī (973-1048):

Ruby mines are situated near the village of Warzqanj which is situated in the direction of Kharukhan while going from Badakhshan at three days’ journey. It is a part of an emperor’s domain, the capital of which is Shakasim, which is close to the mines producing this stone. The approach to the mines via this route is easier, and it passes between Shakkasmi and Shaknan. This is why the governor of Wakhan keeps the most precious jewels for himself, and precious jewels pass this way clandestinely. Jewels weighing beyond a certain size are prohibited from being carried outside the mine, and only stones weighing up to the sizes he has fixed or specified are permitted to be taken out.

It is said that the mine was located when there was an earthquake in the area and the mountain was cloven. Big rocks fell down and everything was destroyed. Rubies were disgorged in the process. Women thought the stone was something with which clothes could be dyed. They ground the stones, but no colour came out. Women showed the rubies to men and the matter was publicised. The king ordered the miners to locate the mine. When they found it they began to excavate it.

al-Bīrūnī 11th Century

al-Bīrūnī was an amazing person, by the way.  A true polymath (renaissance man, genius, righteous dude), al-Bīrūnī spoke Persian, Hebrew, Sanskrit, Greek, Aramaic, Arabic, Syriac, and probably others.  He was a master of physics, astronomy, mathematics, linguistics, is known as the “the world’s first anthropologist”, and the founder of geodesy (the science of accurately measuring the surface, shape, and features of the Earth).  This article isn’t about al-Bīrūnī, but maybe a future one will be, until then read up on the dude, he was amazing.

 Abū al-Rayhān Muhammad ibn Ahmad al-Bīrūnī
The Divinci of his day… I guess Divinci should be called the Biruni of his day since he came afterwards.

I digress… In the early 1970s, Dr. Mira Alekseyevna Bubnova,  an anthropologist from the Tajik Academy of Sciences, found evidence that mining operations may have began as early as the 7th century.  The empire of Shakasim funded and controlled the mining operations for the “rubies” and the local governor of Wakhan managed to keep the best stones for himself.  There were also problems of miners “high-grading”  the nicer stones for themselves (“high-grading”: that act of sneaking big, fancy stones or gold nuggets, etc, out of a mine) and then smuggling them out of the realm.  The laws were fairly strict, only a stone smaller than a certain size was allowed to be removed from the mines, leaving many of the greatest stones right where they were found.

Some of the most famous rubies in the world came from these mines; the Timur Ruby, the Samarian Spinel, and the Black Prince Ruby.  Wars were fought over various crown jewels; the majority of which managed to be coalesced by the Mughal Empire.  The Mughals were a mix of Persian and Mongolian ancestry that were direct descendants of the Genghis Khan.  These warrior lords invaded and ruled much of the Indian subcontinent from the 16th to the 19th centuries.  The wealth of the maharajahs who ruled the empire were legendary.  Portuguese and English sailors who were presented to the courts of these men told the world of the piles of jewels that surrounded them in the throne rooms and of the elaborate, ornate jewelry that adorned the monarchs and their family.  Much of the gold that was discovered in the gold rushes of the Yukon, California, and Colorado went to the maharajahs to create their jewelry; where they traded their lesser stones for the gold.  One particular tradition that began with the Mughal Maharajahs was to inscribe their names on the grand stones.  Some saw this as vandalism while others, like Emperor Jehangir, saw it as a way for their name to live on forever.  In his case, it has.

Rubies and Sapphires were so important to the world’s powers that England overthrew Burma to take theirs.  It was not until gemological sciences started to become more refined by the 19th century, as did all sciences with the Industrial Revolution, that was realized that what we had been calling rubies and sapphires were not really exactly what we thought they were, but different stones that were basically named wrong.  It turns out that there were two stones involved, just not he distinction of rubies and sapphires like everyone thought, but of corundum and spinel.

The problem: Scientists had to decide on their definitions.  Which stone would remain a “ruby”, which stone would remain a “sapphire”, and which stone would get the new moniker of “spinel”.  Well, 150 years later we have our answer.  If it was corundum and red, it was called a “ruby”.  If it was corundum and any other color, science henceforth dubbed thee “sapphire”.  Everything else then became “spinel”.  The downside to this was that the largest red stones in the crown jewels of Iran, Russia, England, France, and India were all ignored as useless because they were no longer “rubies” as previously thought.  Spinel’s problem was that rubies had 4,000 years of marketing behind them, and spinel had none.  If the scientists had decided the other way around and called what are now known as rubies and sapphires “spinels” instead things would have turned out different indeed.

Only recently (in the last decade or so), have spinels started to get noticed in their own right. Jewelers and collectors started seeing the inherent beauty in the wide array of colors of spinels.  Those in the know have also realized how rare these stones actually are.  Historically, gem-quality spinel was only found in three places around the world: Badakshan (Afghanistan/Tajikistan); the gravels of Sri Lanka; and Mogok (Burma/Myanmar).  Two recent discoveries in Luc Yen, Vietnam and in Mahenge, Tanzania have come to the forefront as of late.  Mahenge is the real reason for spinel’s revival.  The discovery of the neon orange/red/pink stones there have driven up prices world-wide with stones larger than 5 carats fetching $10,000 to $20,000 per carat, now rivaling the finest rubies of the same quality and size.

Spinels are usually found in metamorphic rock, marble mostly, all over the world.  There are deposits on every continent, including North America.  It is the discovery of gem-quality stones that evade us here in the “New World”.  You can find examples of ugly, brown cubic crystals of spinel in New York and New Jersey, and Ontario.  There are reports of gem-quality stones in East Fresno County, CA of various colors and sizes–I haven’t seen any yet, nor can I find any photographs of these supposed spinels.

I listed a couple famous spinels from the mines of Central Asia a little earlier.  The current world record holder is the Samarian Spinel at 500cts.  The stone is heavily included, brownish red in color, “polished in the rough”, and worth tens of millions of dollars.  In ancient times spinels, and most stones in general, were polished in their rough form as exact faceting methods where not necessarily invented yet.  In the 18th century, the Persian King Nader Shah captured the stone and its 270ct cousin in an invasion and conquest of India.  There is a hole drilled in the Samarian that was supposedly used to affix it

Pink Mahenge Spinels
Spinels from Tanzania that are famous for their neon characteristics. From Swala gem Traders

around the neck of the Biblical Golden Calf that the Israelites created while Moses was receiving the Ten Commandments.  The problem is that the Samarian was most likely from the mines of Northern Afghanistan and was mined a couple thousand years after Moses yelled at the idol worshipers in Sinai.

The most valuable spinels are as follows: Balas rubies (the stones that were originally thought to be rubies from Afghanistan/Tajikistan); neon Mehenge spinels (a 10ct stone will cost you about $200k!); pigeon blood spinels, usually from Mogok, Sri Lanka, or Vietnam; and cobalt spinels (often from Sri Lanka or Tanzania, they are a steely blue hue and color come from, you guessed it, cobalt!) which can be valued upwards of $5,000 per carat.

Cobalt Spinels
Tanzanian Cobalt Spinels from Pala Gems

This brings us to my big announcement:

I proudly present the new record holding polished spinel:  I am the proud owner of the The Sinful Red Spinel (named such because it is sinfully ugly).  The original stone was 2000cts and was found embedded in white marble in Mahenge, Tanzania.  I received the stone in the rough and polished it myself.  Keeping with the tradition of the great Mughal emperors the Sinful Red is polished in the rough and weighs in at a hefty 689cts crushing the old world record holder!

I have a large collection of Tanzanian and Vietnamese spinels that I will be polishing in the coming months and I look forward to sharing them with you.

10.24ct Ceylon raspberry spinel from Sri Lanka
10.24ct Ceylon raspberry spinel from Sri Lanka. Owned by Noosphere Geologic.

7ct Mogok spinel.
7ct Mogok, Burma spinel. Extremely rare, owned by Noosphere Geologic.