Thursday, July 5, 2007

Sharp mineral dealer discovers extremely rare mineral specimen being used as a paper weight at the Tucson show.

While exploring some remote corner of the Tucson Gem and Mineral Show, Denver based gemstone and mineral dealer Morgan Sonsthagen came across an attractive bright pinkish-orange rock being used as a paper weight. Thinking it was a rhodochrosite he asked the dealer, "how much for that rock on the pile of papers"? The seller claimed that he couldn't sell the rock because it was holding down all of his papers. After a short negotiation, Morgan volunteered to find the guy a new rock for his pile of papers and they agreed on a price for the orange rock.

That 150 gram rock turned out to be triplite, an extremely rare mineral found sparingly at a few localities throughout the world. Morgan suspects that the material is the same as the material from Guilin, China, incorrectly identified as triploidite in Gems and Gemology (summer 2006). Apparently, the only other gem quality pieces come from Pakistan near Dassu and most of those are somewhat brownish in color. Very few if any other triplites are available in the bright orangey colors of Morgan's material and nearly every other triplite deposit only produces grainy granular opaque material.

The rough was processed in Bangkok by Warren Weise at his Thonburi factory. In addition to some smaller stones, two large gems were recovered; a 21.29 ct. pear shape and an 11.05ct. round. Some of the stones were tested at the AIGS gem lab by Dr. Laurent Massi and some of the rough was donated to the RRUFF University of Arizona Mineralogical project for further analysis.

Triplite is a rare fluoro-hydroxide phosphate mineral that forms in phosphate rich granitic pegmatites and high temperature hydrothermal veins. With formula (Mn,Fe2+)2(PO4)(F,OH), calcium and magnesium commonly substitute in the divalent cation site. In color and appearance, triplite can be very similar to rhodocrosite, another manganese bearing mineral and it is most likely the high concentration of manganese that is responsible for the bright peachy color. Chemically, triplite is also quite similar to triploidite the difference being that triplite is F dominant while triploidite is OH dominant.

Triplite was first described in 1813 for an occurrence in Chanteloube, Limousin, France. The name is derived from the Greek triplos for triple, in reference to the three cleavage directions. Other occurrences include the Shigar Valley, Pakistan; China; Bavaria, Germany; Kimito, Finland; Karibib, Namibia; and Maine, Connecticut, Arizona and Colorado in the United States. Triplite is quite rare and difficult to facet do to its brittleness and cleavage.

Only a few cut stones have been reported and all of them are from the Shigar Valley in Pakistan. One specimen from Dudley Blauwet was loaned to the GIA for examination. General absorption to 450nm, weak absorption bands at 470nm and 490nm, and a stronger band at 520 - 620nm were observed with a desk model spectroscope. Microscopic inspection revealed finger print type and two phase inclusions.

Wednesday, January 17, 2007

Some of the the world’s rarest gemstone varieties

Painite has in years past been described by the Guinness Book of World Records as the rarest gem mineral. As of early 2005 there were eighteen known specimens, all numbered and accounted for. Painiteis pink to red to brown in color, very strongly pleochroic (showing different hues from different angles) and it fluoresces a lovely green under short wave UV. It comes from Mogok and Kachin State in Myanmar and was named after its discoverer, British gemologist Arthur Charles Davy Pain.

Serendibite is a cyan colored stone that comes from Sri Lanka. It boasts an unusually complex formula consisting of calcium, magnesium, aluminum, silicon, boron and oxygen. So far there exist three faceted specimens of 0.35 carats, 0.55 carats and 0.56 carats. The first two were discovered by rare stone specialist D. P. Gunasekera and purchased by the late Prof. E. J. Gubelin of Switzerland. The name comes from the old Arabic term for Sri Lanka, Serendib, as referenced in The Sixth Voyage of Sinbad and elsewhere.

Dumortierite is a fibrous variably colored aluminium boro-silicate mineral that is primarily used as an ornamental stone. It has a deep violet to blue color that is quite attractive and unusual. Although rarely used as a gemstone due to its lack of clarity, its hardness and bright color make it useful for the manufacture of all kinds of carvings. Massive dumortierite can be carved into cabochons, beads, sculptures, eggs and spheres. Facet quality dumortierite is extremely rare and few specimens exist anywhere.

Petalite is a colorless and glassy looking but some stones are pale yellow and a pink chatoyant specimen has also been reported from South Africa. Little crystalline material is ever available for cutting and faceted stones are uncommon. Large clean stones are always in demand by collectors. The name petalite is derived from the Greek word 'petalos' meaning leaf, an allusion to the cleavage.

Grandidierite is a bluish green mineral found primarily in Madagascar. The first and so far only clean faceted specimen, from Sri Lanka, was originally mistaken for a serendibite and subsequently purchased in May 2000 by Prof. Gubelin from Murray Burford. The mineral is named after French explorer and natural historian Alfred Grandidier, who among other things unearthed bones from the extinct half-ton elephant bird in Ambolisatra, Madagascar.

Jeremejevite, is a colorless, sky blue or pale yellow stone, the highest quality of which comes from Namibia. In nature it occurs in small obelisk-shaped crystals and has in the past been mistaken for aquamarine. It was named after Russian mineralogist Pavel Jeremejev who discovered the mineral in 1883.

Majorite is a purple form of garnet that was discovered in 1970 in the Coorara meteorite near Eucla, Western Australia. The species is named after Alan Major who researched high-pressure garnet formation.

Taaffeite, is a mauve to purple to red stone named after Bohemian-Irish gemologist Edward Taaffe who discovered the first one from a box of Sri Lankan spinels in 1945. The stone displayed a double refraction which was uncharacteristic of spinel. If you could round up all the faceted taaffeitescurrently in existence they would fill about half a cup.

Musgravite chemically and optically similar to taaffeite but a lot more rarer. Facetable musgravite was first reported in 1993 and as of 2005 there were eight such specimens, three of those identified by Murray Burford. The mineral was discovered in 1967 at the Musgrave Range in South Australia, but has since then turned up in Greenland, Madagascar and even Antarctica.

Benitoite is found only in San Benito County, California. The stone is a strong blue with a dispersion similar to that of diamond, and fluoresces an intense blue-white under UV light.