Monthly Archives: December 2012

Natural Heliodore, Golden Beryl from Connecticut

10986: 2.11 Carat pear shaped brilliant cut with exceptional vivid color and crystal.

by Richard W. Wise, G.G.

10987 A 1.74 Carat ovall brilliant heliodore from the Roebling/Merryall MIne, Litchchfield, Ct. The gem exhibets an exceptional vivid medium toned golden hue.

10987 A 1.74 Carat oval brilliant heliodore from the Roebling/Merryall Mine, Litchfield, Ct. The gem exhibits an exceptional vivid medium toned golden hue.

Golden Beryl; An American Gem

In the 19th Century, the state of Connecticut was known as a major source of golden Beryl.

In the past few years a fair amount of golden beryl a.k.a. heliodor has entered the gem market. Material currently in the market is coming from Pakistan, Brazil and Ukraine and although there is no reliable gemological test that will prove irradiation, much of this material is thought to be enhanced by gamma radiation, a method that leaves behind no footprints. Of late there have been misguided attempts to cash in on the gem's more famous sibling by re-labeling the gem as "yellow emerald."

The continental United States is not known for its gem wealth though historically both California and especially the New England states have produced some exceptional gems. In the 19th Century, Maine was known as a repository of gem quality tourmaline, some beryl and amethyst. Most of the gems found in New England are of pegmatic origin the result of long super-hot magmatic fingers working their way up through cracks into the country rock causing localized melting into a chemical stew and its constituents, where beryllium oxide was present, might reform into beryl crystals. Many of the most important strikes were found in Maine including the famous Mt. Mica Mine which resumed operations in 1990 after a long hiatus. Pegmatites are found in all the New England states excluding Rhode Island and are particularly numerous in Maine and New Hampshire. Gem mining was in most cases simply a byproduct. The mines were mainly exploiting mica, Beryllium and feldspar.

Beryl is a family name whose best known offspring are emerald and aquamarine. If a beryl is pink it is known as morganite if red it is called bixbite or simply red beryl. In the 19th Century, golden beryl was quite rare and Connecticut was considered a major source. The term heliodore, from the Greek meaning "gift of the sun" was originally a trade name made up to describe yellow beryl from Southwest Africa.

"A Gift from the Sun," Gem Mining in Connecticut:

Few realize that the George Roebling or Merryall Mine located in Litchfield County, Connecticut was, historically, one of the most productive and commercially important gem mines in the United States. This mine opened in 1880 as a feldspar and mica mine and worked intermittently until 1955 when it was closed. According to the late John Sinkankas, Merryall is known to have produced particularly fine beryl in shades of blue, yellow and green including a 40.44 blue-green heart shaped gem that now resides in the Smithsonian. The mine produced some sizable aquamarine, but most of the heliodore production was limited to very small faceted gemstones.

We recently acquired a few particularly fine rough examples of natural unenhanced heliodore, portions of a single large crystal, sourced at the Roebling/Merryall Mine site from a pile of unsorted mine run material in the early 1980s. The crystal was inside a large boulder. This material has been precision cut into a few lovely heliodore gems. These gems are flawless to the eye, exhibit a particularly fine crystal structure, a high degree of transparency and a vivid pure yellow hue and perfectly cut by our lapidary.

10987 Rough material from which the 1.74 carat oval, 10987, was cut.

10987 Rough material from which the 1.74 carat oval featured at the beginning of this post, 10987, was cut.

As Sinkankas points out, very little of the material sourced from this location is of gem quality never mind eye-flawless material. Mine run material containing 1% Beryllium is considered a rich deposit. Gems from this site have not been on the market in many years. For the gem collector, this is an or for the jewelry lover looking for a lovely vivid yellow gemstone, this is an opportunity to buy American and acquire a particularly fine gem from a truly rare source.

Gemstone Cut Grading; Distinctions Without a Difference II

Of Tilt-Windows, Off-center culets and other minor issues:

The image of the gem quality 1.44 carat alexandrite might lead the uncritical observer to conclude that the gem is windowed. What the gem is actually exhibiting is some extinction beneath the table. In a perfect world, both are minor faults, but we are talking about the rarest gem on earth. In the world of true rarity, beauty not mathematical perfection of symmetry is the ultimate criterion.

The first time I ever heard the term tilt-window was on the Pricescope forum. As you know, a window is a part of the gem when viewed face-up that exhibits transmitted light. Windows are almost always found right beneath the table. A quick test is to place the stone over a piece of newsprint. If you can read the print, you are looking through a window. Windows are the result of a shallow pavilion, a too shallow depth to width ratio. Windows are considered faults because they are a portion of the gem that does not sparkle.

Gem cuts are designed and engineered to be judged face-up with light perpendicular to the table. Tilt the gem away from the perpendicular and every gem other than a briolette will exhibit a window. Ironically the more precise the cut, the more likely the gem is to window when tilted as little as five degrees from the perpendicular. Some gems, particularly those with a bit of fat around the pavilion, may exhibit some brilliance when tilted as much as ten to fifteen degrees from the perpendicular. What cannot be eliminated must be embraced. A tilt window, forgetaboutit!

Grading; From Minus To Plus:

Gems with bulbous pavilions are often criticized for being overweight, meaning that the stone’s face is smaller than it would be if the stone was perfectly cut. The irony here is that such stones may actually exhibit a greater arc of brilliance which contributes to the beauty of the gem. Once the eye is four to five feet from the gem, the overall brilliance becomes the real issue, not the stone’s mathematical diameter. Broader bellies also extend to the length of the light path and may enrich the color (hue, saturation and tone) of the gem.

In another Pricescope thread, one ubiquitous poster put a link to an alexandrite (pictured above) on my website and criticized me for the failure to disclose an off-center culet. How did this forum member determine that the stone had such a terrible fault? The page included a side view image of the stone face-down. If there was an attempt to hide the fault, it was hidden in plain sight. http://www.rwwise.com/products/id,255 Unfortunately her interpretation of the image was quite wrong. The stone does not have an off-center culet. What the forum member saw was a very minor symmetry fault, one side of the pavilion has a slight indent coupled with a tilted crown which when placed on a flat surface caused the culet to appear off-center. And if the gem did have a slightly off-center culet, so what! We are talking about one of the earth’s rarest treasures, a gem quality alexandrite!

Each Gem Is an Individual with a distinct personality and should be judged on its merits:

Gem aficionados usually begin their love affair with the colorless diamond. They learn the famous 4 C’s and attempt to apply those criteria, namely color, clarity cut and carat weight uncritically to colored gemstones. As I have said elsewhere all Cs are not created equal. In the connoisseurship of colorless diamond, cut is the 1st and most important criterion. Diamonds have no color, they are all about brilliance and sparkle, so naturally cut, which delivers sparkle is the most important single criterion. I knew a neophyte jeweler once who was not satisfied with eye-flawless sapphires, he demanded that all of his sapphires be flawless under 10x magnification. The problem, without inclusions it is almost impossible to determine if a stone has been enhanced and determination of geographic origin is absolutely impossible.

Colored gemstones as their name suggest are all about color and cut is, at best, a secondary consideration. An off-center culet in a diamond would be a major symmetry fault and materially effect price. In a colored gem, an off-center culet in and of itself is a minor fault which has no effect on price. Why do such things exist? A culet might appear off-center for a couple of reasons. The lapidary may have removed a potentially eye visible inclusion or have placed the culet slightly askew to smooth out color zones so that the zone does not appear in the gem when viewed face-up.

It should be remembered that colorless diamonds are not truly rare. The introduction of cut and clarity scales that have nothing to do with beauty are more about creating the appearance of rarity than the thing itself. The connoisseurship of gemstones requires discernment and careful contemplation. Gems cannot be accurately graded by image. The aficionado should beware attempts to reduce it to a formula or a check list.

Gem Cut Grading; Distinctions Without A Difference

A Non-Issue:

This is a good example of a non-issue. Non-symmetrical cuts, rectangle, oval, pear viewed under a single beam light source will always show brilliance across half the face of the gem when the stone is tilted away from the perpendicular. Why, because the gemstone is not symmetrical and therefore treats light in a non-symmetrical fashion. In the cuts just mentioned, some facets particularly the pavilion facets which are responsible for delivering brilliance, cannot be uniform. Some are larger, some are longer therefore light hitting these facets will refract in an irregular fashion. Symmetrical cuts, rounds and square cushions, by contrast have uniform facet patterns and do not suffer this phenomenon.

For this reason, asymmetrical gems are graded under a single light source, viewed at at a 45 degree angle away from the light source angled toward the eye. At this viewing angle, half the gem, the bottom half is potentially brilliant. The percentage of that half is then compared with the other half when the gem is rotated 180 degrees and viewed a second time. Add the relative percentage of each half and voila you have the total percentage of brilliance. In colored gemstones, 80% brilliance is considered excellent which means that at any given time, 20% of the gem will exhibit extinction.

One trick for viewing the brilliance of the entire stone at once is the use of sky light. Turn your back to the sun and view the gem at the same 35 degree angle toward the eye. In this position the light filtering around the body of the viewer should light up the 100% of the gem. Any lack of brilliance in this position is a fault and should be subtracted from the theoretical 100% to arrive at the percentage of brilliance. In most cases, gem photographers correct for this phenomenon by photographing gems with non-symmetrical outlines by using multiple light sources.

A Little Extinction Contributes To A Gem’s Beauty

Extinction is another much misunderstood phenomenon. I am often asked, particularly by members of this forum, if a particular gem shows extinction. First lets define our terms, what is extinction. This phenomenon is caused by off-axis refraction. When light enters a gemstone, it enters the crown and reflects internally off the pavilion (back) facets and eventually back through the crown to the eye. Inevitably some light refracts at an angle that is not toward but rather away from the eye, the greater the angle the more extinct it becomes, in a tonal continuum from gray to black.

All faceted gemstones without exception exhibit extinction, no extinction, no scintillation. the great German philosopher Hegel said determinatio est negatio. which when reduced to simplest terms means g all positive requires a negative. Sweet has no meaning without salty, good does not exist without evil, etcetera. So too with gems. Scintillation, sparkle is the result of light being broken up into pieces, tiny scintillas of light that are refracted back to the eye in little pieces. Between those pieces is darkness, extinction. Want a gem to light up like a flashlight with no sparkle, eliminate extinction. Some degree of extinction is therefore required as contrast.

Extinction As A Fault:

Extinction can have other causes as well, dark is the absence of light. Gems lacking transparency will often show what one of my clients once called a “heart of darkness” at the center of the gem beneath the table. This is particularly prevalent in sapphire and the cutter will often cut a window to let in light through the culet, the apex of the cone shaped pavilion of the gem. So while some extinction is desirable, in fact necessary to the beauty of the gem, large areas of extinction are a definite and definable fault.