Not without some controversy and easily finding several different listing on various sites on the internet, lets look at 10 Faceted Gemstones that can stir up debate about them being the 10 rarest. But whatever list one uses, they all have one thing in common - they are all very very expensive.
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PAINITE has been described as the rarest gem mineral. As of early 2005 there were eighteen known specimens, all numbered and accounted for. Specimen No. 5 has been faceted into an oval and weighs 2.54 carats. Painite is 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..
SERENDIBITE, not to be confused with serandite, 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. The name comes from the old Arabic term for Sri Lanka, Serendib, as referenced in The Sixth Voyage of Sinbad..
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POUDRETTEITE, another of the purple gemstones from Magok, Myanmar, was discovered in 2000. By December 2004 nine gem-quality pieces had been found , including a pale pink. At a Mohs hardness of 5, Poudretteite is the softest stone on this list — too scratchable for a ring but suitable for earrings, a pin or a pendant if care is exercised. Previously this substance had been known as a rare mineral of tiny colorless crystals, discovered in 1987 and named after the Poudrette family that operated the source quarry at Mont Saint-Hilaire, Quebec.
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POUDRETTEITE, another of the purple gemstones from Magok, Myanmar, was discovered in 2000. By December 2004 nine gem-quality pieces had been found , including a pale pink. At a Mohs hardness of 5, Poudretteite is the softest stone on this list — too scratchable for a ring but suitable for earrings, a pin or a pendant if care is exercised. Previously this substance had been known as a rare mineral of tiny colorless crystals, discovered in 1987 and named after the Poudrette family that operated the source quarry at Mont Saint-Hilaire, Quebec. 
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. Grandidierite is trichroic, transmitting blue, green and white light. 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.
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 forms under the extreme pressure that occurs 250 miles (400 km) or more beneath the earth’s surface or from the shock of a meteorite impact. It’s a dark 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. Has similar formation to the apple green Moldavite collected from around a metor strike in the Czech Republic.
.MAJORITE forms under the extreme pressure that occurs 250 miles (400 km) or more beneath the earth’s surface or from the shock of a meteorite impact. It’s a dark 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. Has similar formation to the apple green Moldavite collected from around a metor strike in the Czech Republic.
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 taaffeites currently in existence they would fill about half a cup. Of the rarest red variety there are fewer than ten specimens. .
MUSGRAVITE is a species chemically and optically similar to Taffeite, but is even rarer. Facetable musgravite was first reported in 1993 and as of 2007 there were eight such specimens. 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. It’s not unlikely that some stones thought to be taaffeites by their owners are actually musgravites. Micro-Raman spectroscopy, which uses a green laser, can quite handily distinguish the two.
MUSGRAVITE is a species chemically and optically similar to Taffeite, but is even rarer. Facetable musgravite was first reported in 1993 and as of 2007 there were eight such specimens. 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. It’s not unlikely that some stones thought to be taaffeites by their owners are actually musgravites. Micro-Raman spectroscopy, which uses a green laser, can quite handily distinguish the two. .
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. The largest faceted Benitoite weighs 15.42 carats, but stones over one carat are rare. In 1974 someone stole a flawless 6.52-carat pear-shaped specimen from the Zurich airport and it’s still missing. In 1985, Benitoite was designated the state gemstone of California. PHOSPHYLLITE is a rare mineral composed of hydrated zinc phosphate. Its name derives from its chemical composition (phosphate) and the Greek word for "leaf", phyllon, a reference to its cleavage. It is highly prized by collectors for its rarity and for its delicate bluish green colour. Phosphophyllite is rarely cut because it is fragile and brittle, and large crystals are too valuable to be broken up. The finest Phosphophyllite crystals come from Potosi, Bolivia, but it is no longer mined there. Other sources include New Hampshire, USA, and Hagendorf, Bavaria, Germany. It is often found in association with the minerals Chalcopyrite and Tripholite.
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The above listing appears to be based on the hardest to find, finding sizes to facet and somewhat on pricing. There are other listings of the 10 rarest gemstones based solely on price, hardest to find, exotic and lack of availability. The following list is based on a 2008 cost per caret. Please note several are repeated from the above list.
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Jadeite $3+ million/caret
Red Diamond $2-2.5 million/caretSerendebite $1.8-2 million/caret
Blue Garnet $1.5 million/caret
Grandidierite $100,000/caret
Painite $50-60,000/caret
Musgravite $35,000/caret
Red Beryl $10,000/caret
Black Opal $2,500/caret
Jeremejevite $2,000/caret
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some even add Tanzanite to this list at $1,800-2,200/caret.
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And then we must not forget the most popular gemstone: which by it's pricing would quickly make one think it is rare:
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DIAMONDS, in general, Diamonds are not at all rare, but controlled pricing keeps the price high. The De Beers Company would prefer you didn’t know, but annual world production of gem-quality Diamond exceeds sixty million carats. This equals twelve metric tons and would fill about 145 bushel baskets. Consider this the next time you pony up a few thousand dollars for an engagement ring stone. However, colored Diamonds, called fancies, can be genuinely scarce. About one carat out of every 10,000 sold is a fancy. These shades include yellow, green, blue, orange, brown (“champagne”), purple, gray, black (called carbonado, recently shown to be meteoric), milky white, pink and red. Red is by far the rarest.
.Thanks to several gemology friends for information and pictures of the rare gemstones, although still missing a couple pictures.
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