Hello Peter & Chuck
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The following may also be of interest.
June 4, 1997
How do I tell the difference between diamond and moissanite?
First, let's let everyone in on what moissanite is. Moissanite (carborundum, SiC) is a natural but VERY rare mineral named after Nobel Prize winner Dr. Henri Moissan who discovered it in an Arizona meteorite called Diablo Canyon. While moissanite is an exceptionally good imitator of diamond, there has been so little natural material found that it has been insignificant in the gem and jewelry world. Till now, perhaps...
Synthetic (lab-grown) moissanite is about to be marketed (Summer, 1997, they say) by a company in North Carolina called C3, Inc. The material was originally developed by Cree Research for defense and semi-conductor applications.
Moissanite is very much like a diamond. Its 2.65 refractive index makes it similarly brilliant to diamond (at RI 2.42). Its 9.5 hardness is close to diamond, too (diamond is 10). Jewelers have long used a device called a thermal conductivity meter to separate diamonds from other materials (most refer to these as "diamond testers"). These will not work to separate moissanite from diamond as they both have high thermal conductivity factors. We're told that C3, Inc. is developing a special piece of test equipment to recognize moissanite.
But all is not lost. Some relatively easy gemological tests will separate moissanite from diamond:
Diamond is singly refractive, moissanite doubly (polariscope).
Unique white ribbon-like inclusions in the moissanite.
Diamond's specific gravity is 3.52, moissanite's is 3.20 (not as easily done as the other two tests).
Good luck! I'm somehow reminded of the phrase "the price of freedom is eternal vigilance".
Diamond Simulants in Order by Fire
Diamond is the most often imitated/simulated gemstone in the jewelry market. Here are the materials most often used, in order from least fire to most fire:
1. Fluorite
2. Quartz
3. Topaz
4. Synthetic sapphire
5. Synthetic spinel
6. YAG (Yttrium Aluminum Garnet, a synthetic material)
7. Glass
8. Zircon
(9. Diamond)
(10. Synthetic diamond)
11. GGG (Gadolinium Gallium Garnet, a synthetic material)
12. Cubic zirconia (CZ)
13. Lithium niobate
14. Strontium titonate
15. Synthetic rutile
From #11 on, the materials actually have more fire than diamond, but of course are lacking in other respects such as durability, hardness, and luster.
There is a difference between a synthetic gem and an imitation. Synthetic is the genuine article only it's made in a lab. An imitation is something else altogether that merely looks like the genuine article.
March 27, 1996
What's the highest price ever paid for a gemstone?
There are two ways to quote "price" with gemstones. One is price per carat. The other is price for a given stone. A 2-carat diamond might be quoted as "$4,000 per carat" or "$8,000 for the stone." The highest per-carat price ever paid was for a red diamond at $924,000 per carat. The stone weighed only 0.95ct, was not well cut, and was fairly heavily included - but it was RED. Reportedly, the stone was resold to one of the world's leading gem collectors, the Sultan of Brunei (a small oil-producing enclave near the island of Java in the Pacific). Red is the most rare of all the colors in which diamonds occur. The GIA (Gemological Institute of America) has never identified a diamond as pure red, and only four diamonds' color has had the word "red" in the description: a 2.33ct fancy brownish orange-red, a 0.95ct fancy purplish red, a 0.54ct fancy reddish-purple, and a 5.03ct fancy orange-red brown. I'm not sure what the greatest amount ever paid for a stone was, but since some of them get to be very large indeed (hundreds of carats), it's probably quite high. A 7.37ct intense purplish pink diamond recently sold for just over $6 million, coming in second for the highest per carat price ever paid at auction (at $815,725 per carat). Also recently, a 100.10ct pear-shaped diamond sold for $16,548,750. Ouch!
Diamonds from the Laboratory
It had to happen eventually. And now it has. Chatham (of lab grown emerald fame) recently announced that they would soon be manufacturing and selling laboratory-grown gem-quality diamonds. Initially, they'll be producing only 100 carats or so per month in stones up to 1.5ct each, a very insignificant volume compared to the world diamond demand. Chatham will be producing these diamonds at a facility in Russia, and they will sell only the faceted finished product (no rough).
These lab-grown diamonds will be produced in a variety of colors including white (colorless), yellow, blue, and red. Red, of course, is an extremely rare color for natural diamonds. The largest price-per-carat ever paid for a gemstone was for a red diamond that weighed less than one carat, was full of inclusions, and wasn't particularly well cut. Reds are rare enough that "lab-grown" should immediately pop to mind if you see a clean one of any size and reasonably intense in color.
More recently, Tom Chatham has indicated that his announcement may yet be a bit premature. Working within the new systems of Russia have proven difficult and hard to predict. He cautioned that it may be some time before his commercial production can begin.
Lab grown diamonds do exhibit some characteristics which gemologists can use to separate them from natural. Metallic inclusions (remnants of the flux in which the diamonds form) may be present in sufficient quantity to cause a magnet to attract the stone. Patterns of color zoning separated by sharp boundaries will expose a cubic growth pattern typical of lab-grown diamonds observed to date; naturals grow in somewhat more complex shapes such as octahedrons. Lab-grown diamonds may also exhibit a unique reaction to ultraviolet light, including being stronger in the shortwaves than in the longs (naturals are the opposite).
We'll let you know if we get any...
Structure is Everything in Graphite and Diamond
What two minerals couldn't be more different but are both made of one and only one - and the same - element? The answer is diamond and graphite, both of which are made entirely from carbon.
The only difference between the two is how the carbon atoms are structured internally. Nature determines which of the two forms carbon takes by virtue of the environment during crystal growth, primarily temperature and pressure. At the higher temperatures and pressures, the carbon atoms are packed more densely as diamond. Lower, and the less well packed graphite is formed. The planer nature of graphite is obvious in the diagram, and explains why graphite is a good lubricant - it "slips" readily along those planes.
Diamond Graphite
----------------- ---------------
Composition C C
Hardness 10 1
Color colorless, many grey to black
Optics transparent opaque
Streak color none grey to black
Crystal structure isometric hexagonal
Luster adamantine metallic, dull
Density (SG) 3.52+/- 2.2+/-
Distance between atoms 0.154nm 0.145nm within a plane
0.335nm across planes
(nm=nanometer, one billionth of a meter)
By the way, there are two other (rather obscure) pure-carbon minerals: chaoite and lonsdaleite. Both are trigonal, and are associated with meteorites.
Black Diamond
One of the oddest members of the gem world is the black diamond.
For as rare as they are, and as difficult to cut, you might think they'd command a hefty price. Not so. Very few actual sales have cracked the $1000/ct barrier (despite claims of much greater value). The truth is, they are just not that pretty. Black onyx is really a better choice for this look.
But they are a wonder. What makes a diamond black? What kind of diamond would boast lack of transparency as a plus?...
Exactly how black diamonds are formed is unknown. The speculations have to do with alternating environments (temperatures and pressures) that keep the carbon structure confused. Am I graphite or am I diamond? The back and forth schizophrenia results in a diamond full of graphite (or is that graphite full of diamond? No, I was right the first time...). Anyway, it's this confused internal structure that not only makes the stone repel light but also makes black diamond exceedingly difficult to cut and polish.
You may see a black-looking diamond that actually is a very dark green. These can be made by irradiating a stone through normal greens all the way to a green so dark it appears black - but it's not a true black diamond.
Two well-known black diamonds are the "Amsterdam," a 33.74ct pear-shape diamond; and the 67.50ct cushion-cut "Black Orlov."
Also came across some more info on use of radar in exploration but computer crashed and lost it. Will have to resleuth it this weekend perhaps.
Have a good one.
Regards |
