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Here’s for eccentricity. Outside of mineralogical and
metaphysical circles it’s a pretty safe bet most people have never heard
of any of these. Alphabetically they are
evenkite,
hackmanite,
haüyne,
icosahedrite,
lonsdaleite,
muromontite,
pezzottaite,
proustite,
shungite, and
thortveitite.
That last item is especially perplexing in that we can be absolutely sure it’s either
(1) a genuine, once-in-a-lifetime anomaly, or (2) a clever though unfathomable hoax.
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EVENKITE is most likely the lightest non-porous naturally occurring mineral. At 0.87 grams
per cubic centimeter it floats in water. It’s a clear, waxy crystal of
tetracosane (the 24-carbon/50-hydrogen chain seen to the left) found in
Komna, Czech Republic; Kitaa Province, Greenland; and in the Tunguska
River Basin in eastern Siberia. The name honors the Evenki people.
There are three more ultralight hydrocarbon minerals akin to evenkite and
similarly obscure. In order of increasing weight they are dinite, fichtelite, and
hartite with densities approximating
1.02 gm/cc, 1.03 gm/cc, and 1.05 gm/cc respectively. Dinite and hartite both
have 20 carbons; fichtelite, 19.
All three are colorless when pure and show up in petrified
wood. Dinite comes from Tuscany, fichtelite from
Bavaria, and hartite from Tuscany and Austria.
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One of the weirdest properties in the gemstone repertoire is something called
tenebrescence or reversible photochromism. That’s when the color changes
from exposure to light, like self-adjusting sunglasses, and then
back again after a period in darkness. Several other stones will do this but HACKMANITE, especially some of the varieties
from Afghanistan and Burma, carries this effect to extremes as you can see to the left:
deep purple by day, pale blue by night.
A member of the sodalite or “Princess Blue” group,
hackmanite distinguishes itself by the additional presence of sulfur in
its makeup. Though discovered in Greenland way back in 1896 it’s still relatively
unknown. It’s too soft for a ring or any other application that may take
much of a beating, but fine for something like a pendant. It glows orange to red under UV.
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Another sodalite species, HAÜYNE (ah-ween) has sulfur like
hackmanite but also incorporates calcium, bound water, and sometimes potassium. One of the more rarely
isolated components of lapis lazuli, haüyne is mostly famous for its
almost supernatural-looking blue color.
That splendor comes at a premium, though, since like hackmanite
haüyne’s fragility (a Mohs hardness of 6.5 to 7 combined with some brittleness)
largely confines it to pendants, brooches, and such or genteel show-and-tell among
collectors of the exotic. René Just Haüy (1743-1822) was a pioneer
in crystallography and narrowly missed the guillotine during the
French Revolution.
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ICOSAHEDRITE, which took ten years of focused exploration to discover, so far
appears to be our planet’s only naturally occurring quasicrystal. While the
atomic layouts of all other crystalline minerals consist of
repeating patterns, icosahedrite manages to
sidestep this principle yet still exhibit an ordered lattice.
A good visual analogy would be the Penrose floor pattern you see to the
left. Each tile connects to its neighbors according to strict
rules, yet no matter how hard you look you’ll find no periodic replication in
any direction.
Icosahedrite was found in Russia’s Kamchatka region in the form
of tenth-millimeter grains mixed with serpentine. It’s an opaque, metallic-looking compound of
aluminum, copper, and iron. Along with everything else, researchers are now
certain icosahedrite is extraterrestrial. The bodies that brought it here
were carbonaceous chondrites roughly similar in composition
to Mars’s moons Deimos and Phobos.
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Speaking of extraterrestrial, there’s a powerful contender for the title of
Hardest Natural Mineral called LONSDALEITE. Like diamond it consists of pure
carbon; but while diamond is an octahedral crystal londsdaleite
is hexagonal. The granules found in the wild fall well short of diamond’s
Mohs hardness of 10. But since claims for pure, lab-grown lonsdaleite
routinely exceed 15, maybe it’s just a matter of scoring higher-quality
material out there.
The story began in 1967 when mineralogists first identified its crystals, intermingled
with diamond within the ejecta from Meteor Crater in
Arizona. Since that time lonsdaleite has turned up in meteorites from India,
Antarctica, Australia, and Ontario and from soils in Ukraine, the Kola
Peninsula, the Tunguska explosion area, and elsewhere. The stuff is
translucent and brownish but in most other ways quite diamond-like.
Lonsdaleite’s name honors diminutive X-ray crystallographer and chemistry professor
Kathleen Yardley Lonsdale (1903-1971). “It makes me feel both proud and
rather humble that it shall be called lonsdaleite,” she remarked. “Certainly the
name seems appropriate since the mineral only occurs in very small quantities
(perhaps rare would be too flattering) and it is generally rather mixed up!”
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Strange but true: Any uranium or thorium ore may harbor microscopic wisps of
plutonium and/or neptunium, as both can arise from natural radioactive decay.
About one part per trillion of plutonium was in fact secretly discovered by
Berkeley physicists in pitchblende in 1942. MUROMONTITE, though,
bears the distinction of being the most plutonium-rich of anything found so far
in the ground.
Among radio-minerals, muromontite is a special case. A particular Swedish variety of it
juxtaposes its uranium (element 92) with beryllium. As the uranium decays, some
of the alpha particles it radiates get absorbed by the beryllium. The beryllium
in turn ejects a neutron. When a uranium nucleus gets a square hit from one or
more of those neutrons it can transmute up to plutonium (94), or even more rarely neptunium(93) and
americium (95). Naturally occurring transuranics like these lie far below any
rational threshold of concern. What’s troubling is the 20 tons or so of plutonium
the nuclear industry churns out annually.
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The beryl variety PEZZOTTAITE is particularly special in view of its lithium and
cesium content, the departure from its siblings (aquamarine, emerald, heliodor,
etc.) of its crystal structure, and its lovely magenta color. It was discovered
about ten years ago in Madagascar but that source has run dry. Pezzottaite generally
comes with moderate to heavy inclusions, in the latter state often cuttable into
stunning cat’s eyes. Unlike most gemological exotics it’s durable
enough to wear without much worry.
Dr. Federico Pezzotta is Curator of Mineralogy at the Museum of Natural History
in Milan. He lectures widely and has authored or co-authored
Beryl and Its Color Varieties,
Madagascar: A Mineral & Gemstone Paradise,
and The Italian Island of Elba: A Mineralogical Jewel in the Tuscan Archipelago.
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If you’ve ever seen PROUSTITE (“ruby silver”) it was likely tucked away in
a special booth in the mineral section of a museum. Pushing a button
activated a light to give you a quick peek.
The reason for this cloak and dagger is that proustite is nature’s version
of photographic film. Freshly excavated, the choicest crystals are transparent and
spectacularly red with a metallic luster. But intemperate exposure to light over
time makes them cloud up and blacken permanently. Proustite is a compound of
silver, arsenic, and sulfur and you’re basically seeing the silver take over.
In or out of the dark this mineral is much too delicate for any kind of jewelry
and although a wary cutter may facet it occasionally — for the sake of
novelty — most collectors would freak out at the notion of sacrificing their
specimens that way. Proustite gets its name not from Marcel but Joseph Proust
(1754-1826), a French chemist who established the Law of Proportions for compounds.
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So what’s your favorite form of coal?
There’s something called SHUNGITE being marketed quite breathlessly these
days through the New Age circuit. You’ll find it polished into the shapes of
pyramids, cubes, eggs, spheres, various talismans, and, for the budget-minded,
freeform tumbled stones. It’s touted as a water purifier, cure-all, evil-repeller,
virility-reinvigorator, and so on and so forth. I’d save my money.
But the glassy variety of shungite found around Lake
Onega in northwestern Russia is indeed quite special for a mineral as it most
certifiably contains fullerene molecules. Those are the hollow spheres of carbon
atoms, first identified in 1980 and subsequently named after futurist
Buckminster Fuller.
Right now fullerenes, especially those of the classical 60-atom version
shown to the right, lead some cutting-edge research in a number of technologies.
Pure synthetic C60 costs around $18,000 per pound. A few years ago
there was talk of procuring fullerenes far more cheaply by refining them from
shungite, but in the final analysis the stuff fell
a dispiriting number of decimal places shy of offering enough to
justify such a scheme. An interesting thought, though. Sort of like getting
plutonium from muromontite.
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One fine day in 2004 a purplish pebble turned up in Bangkok in a batch of rough
gemstones from Africa. It fell to the floor at one point and split off
a fragment, which was saved. After the stones were all cut, a routine series of
tests revealed that the purplish one didn’t resemble anything previously known.
The fragment was taken to the Natural History Museum in London and analyzed with
a Cameca SX50 electron microprobe, then it and its faceted 10-carat parent were further scrutinized with a Raman spectrometer at Kingston University. The study as reported by the team of Chapman, Mercer, Rankin, and Spratt
identified the samples conclusively as THORTVEITITE (tort-vi-tite), an
otherwise unremarkable mineral that’s a rich source of scandium.
But no one has ever seen that mineral in the form of a beautifully clear,
facetable gemstone. Unless other thortveitites have been floating around,
misidentified as other species, this would be one-in-a-trillion. Ultrapure
thortveitite can be synthesized, to be sure, but this stone shows mild
inclusions suggestive of a natural source.
It shouldn’t be hard to fake a river-jostled pebble with a few imperfections.
But then how could such an object have ended up in that package of rough, with
the perpetrator assured ahead of time it would be noticed and so painstakingly
analyzed and announced to the world? And how would he or she have ever profited?
It’s been a few years now and no other specimens
have surfaced.
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» World’s Rarest Gemstones »
World’s Rarest Metals
World’s Rarest Things
Today’s Date in a Kazillion Languages
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| Text © Peter Blinn |
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