Mexico's Mystery Stone
Is It Just Lovely and Mesmerizing, or Mystical Too?
by Bob Jones, Senior Editor Rock&Gem Magazine
You may have seen a new lapidary material being offered for sale recently. It's called "Nebula StoneTM," and is a dark-green, nearly black, shiny material with fascinating, light-green, swirling orbicules scattered through the dark matrix. These inclusions make the rock look like the night sky viewed through a telescope, wherein you see galaxies, nebulae and individual stars scattered against a dark background--hence, the name Nebula Stone. It hails from down Mexico way.
|Photo by Jeff Scovil
||Photo by Jeff Scovil
Nebula Stone is certainly an unusual and handsome lapidary material. It is found in large enough masses so it can be worked in a variety of ways. It is not mined by blasting, so has few cracks or stresses that can affect specimens as they are worked.
The material is tough enough to work easily without spalling or chipping, and it takes a good polish. It can be cut and shaped, carved and slabbed. It's yet another good material in the lapidary's repertoire.
What makes Nebula Stone so unusual is that it has been analyzed by several noted scientists without anyone coming up with a definitive answer as to what type of rock it actually is. Using a variety of recognized techniques, scientists have studied the rock carefully, yet cannot come to a final, similar conclusion.
Ron and Karen Nurnberg, the rockhounds who found this unusual gem material on one of their frequent trips to the wilds of Mexico, decided to do things right before marketing Nebula Stone. So they sent samples to Leslie Hale, museum specialist, Smithsonian Institution; Dr. George Harlow, American Museum of Natural History; Sid Williams, head of Globo de Plomo Research Lab; Dr. Dave Douglass, retired researcher, UCLA; Virgil Leuth, New Mexico School of Mines; and Dr. Bruce Geller, associated with Geo Concepts, Unlimited. Clearly, these are highly qualified and well-regarded scientists. Each examined the new material and came up with variations on a theme--one originally developed by Sid Williams.
Williams carefully studied a sample of the material and concluded that Nebula Stone is a quartz pentellerite formed as "a glassy unit that devitrified slowly under quiescent conditions."
Shown at right is eye detail from similar material which the Nurnbergs have dubbed "Supernova Stone."
What this means is that the material was once molten and glass-like but cooled very slowly, allowing the discrete minerals to begin to separate out and crystallize so the final product had lost its glass-like condition. This allowed the orbicules (or spherulites, if you prefer) to form as the different component minerals cooled and crystallized at various rates. It is these little clusters or spherulites of discrete minerals which give the sky-like appearance to Nebula Stone.
The minerals of which Nebula Stone are made include quartz, anorthoclase feldspar, riebeckite and aegirine. The first two form the groundmass of the gem, while the latter two are an integral part of the spherulites.
All this suggests that the rock is igneous. But other research suggests it may be metamorphic, a tentative conclusion reached by work done at the American Museum of Natural History. The American Museum sample also revealed the presence of zircon in the structure. The American Museum people concluded that the rock was not a type of jade, though it does resemble jade, and the original study done at the Smithsonian concluded it was a form of jade. But later work there refuted that conclusion.
Dave Douglass also came up with the conclusion that the rock was a form of jade. He called it chloromelanite, a green- to black-flecked variety of jadeite. He based his conclusions on x-ray dispersion analysis (EDX) in a scanning electron microscope. He also used x-ray diffraction on the samples. The lack of magnesium and calcium in the green areas he studied eliminated nephrite jade as a possibility, while suggesting a jadeite conclusion (yet to be verified).
Bruce Geller has done very extensive work on the material. He did numerous thin-section studies, which indicated a metamorphic origin for the rock. He also suggests the presence of acmite (a pyroxene) and even a trace of epidote.
Rather than reaching one conclusion, Geller suggests a couple of possibilities. He does rule out jadeite. Instead, he suggests that the rock could be a low-grade metamorphic type which could have originally been a basalt or chert. Another suggestion he makes is that the rock could have started out as a syenite, ending up as a pyroxene-feldspar schist.
One of his final comments really best sums up what is known about the rock so far. "I found this sample to be [deceptively] complex and challenging for its science." Well said!
Virg Leuth originally concluded that the material was metamorphic but, after further study, concluded the rock has an igneous origin. His work with a petrographic microscope and x-ray diffraction found yet another mineral--arfedsonite, closely related to aegirine--in his sample.
Though these tentative conclusions seem to vary widely, they can all be accounted for when you realize that each scientist was working with a different sample, or samples, not necessarily gathered from the same exact spot in the formation. With different testing methods also employed, along with different means of sample preparation, you can readily see why there is a variety of conclusions--conclusions which can only be refined and finalized upon further study.
What is important for the rockhound is to know that these scientists do agree on one thing: This is definitely something new, different and yet to be described in the scientific literature. This is exciting stuff for a couple of weekend rockhounds who had the intelligence to recognize a unique material during their rock-collecting forays and then, instead of rushing to capitalize on their discovery, had the good sense to recruit scientific help in establishing the identity of their find.
Shown at left is one of the larger masses of Supernova Stone recovered so far by Ron and Karen Nurnberg. This material exhibits prominent and striking eye marks similar to Nebula Stone, but is much rarer and is typically found as larger pieces. When cut it shows quite a range of patterns. Photo by Ron Nurnberg.
Though not yet conclusively identified as to rock type, Nebula Stone has certainly been identified by the discoverers as a good lapidary material, suitable for a variety of uses . . . and this by a different set of experts: people who actually work with gem rough! Its unusual eye-like spherulites can be related to the ancient belief in the all-seeing eye which has been a continuous symbol of many religions and incorporated in many belief systems extending back to very ancient times.
From the research so far we can make some interesting scientific conclusions. Though several experts have done initial studies on the stone, there seems to be no one conclusion that can yet be drawn as to Nebula Stone's rock type. Part of the problem is that the scientists have been using only a limited number of samples. As mentioned earlier, collecting techniques, the variety of test equipment used, individual interpretations and more can account for the obvious variations in test results. One sample may contain a trace of epidote, for example, while others may not. And so on.
We are left to wonder, is there zircon in the stone or not? Is the black included mineral aegirine or riebeckite, or are they both present? Is there a possibility the rock is a type of jadeite or is it quartz pantellerite, as Williams suggests?
If you draw no other conclusion from this report you should be impressed with the considerable variety of esoteric and very sophisticated equipment employed to study rocks and minerals. Such machines as the scanning electron microscope (SEM), back-scattered electron detector (BSE), and the electron microprobe, along with thin-section study and the like will eventually ferret out the truth. These tools are readily available at universities and in laboratories and they have been of immense help in developing an understanding of the earth's composition.
Yet, it is also obvious that in spite of the variety of equipment employed, coupled with the expert knowledge of scientists, the identification of some rocks and minerals is no easy task. My hat's off to the experts who, with great patience, vast abilities and perseverance have given us so extensive and accurate a picture of the earth today.
Again, since this is a relatively new gemstone, information on how it can be polished or tumbled is important. As for polishing, carver Lee Worthington suggests using tin oxide with a little vinegar and a pinch of Linde A--all this on leather.
As for tumblings, Ron suggests starting with 80-grit and tumble for four days. Rinse and clean and repeat the 80-grit for four days. From there, do four days each of 250-grit and 400-grit, being sure to wash and clean between each operation. Then shift to 600-grit for seven days and the stones will be ready to tumble polish. This is done with either tin- or cerium oxide.
You might be interested in knowing just how Nebula Stone was found. Ron and Karen, who are from Sierra Vista, Arizona, were hiking in Mexico, following an old path in the mountains, when they entered a hidden valley which they describe as follows:
"Everything appeared lush and vibrant, and there were many old trees watching over the valley. We felt as though we had entered a very special place--almost magical. The sounds and colors seemed enhanced and even the birds and animals seemed curious. We had never found any place quite like this before. . . . unusually serene and peaceful."
It was in this ideal setting that they found their first example of Nebula Stone, a stone now enjoyed by the mineralogist, the lapidary and the spiritually inclined alike.
You can obtain further information on Nebula Stone at the Nebua Stone web site.
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