All gemstones can be considered rare, especially since they constitute only a tiny fraction of the total minerals found on the entire earth's surface (or under the surface). However, some gemstones varieties should be considered extremely super rare, because there are only a small handful of gem-quality specimens known to exist in the entire world for some gem types.
Very rare gemstones hold a special interest for all gem collectors and connoisseurs. Most rare gemstones are simply rare specimens of a more common species or type, such as ruby or sapphire. For example, a very clean pigeon-blood ruby from Burma over 5 carats would be very rare, but ruby in general is a common gem type athough it is still one of the more precious of gems. However, there are some gemstone types, which by themselves are so rare, that any gem-quality specimen would be considered as being extremely rare.
Red diamonds are the most rare and valuable of all gemstones, with fine specimens selling at auction for over $1 million per carat. The largest known red diamond is the Moussaieff Diamond, which weighs in at 5.11 carats and was graded by the Gemological Institute of America (GIA). The diamond's rare red hue was generated from microscopic defects within the crystal lattice. The diamond was later purchased by the William Goldberg Diamond Corp., where it was referred to by its original name, the Red Shield. The rare red diamond is now currently owned by Moussaieff Jewelers Ltd. The selling price was never revealed. Red diamond is suitable for any type of jewelry design, especially since diamond is the hardest substance, grading a 10 on Moh's scale of hardness.
Painite is a rare type of borate mineral that was first discovered in Burma by British mineralogist, A.C.D. Pain, in 1954. These rare gem specimens contain zirconium, boron, calcium, aluminum and traces of vanadium and chromium. Painite is relatively hard and rates an 8 on the Mohs scale. Until 2005, only 25 crystals were known to exist and only a few gemstones specimens were faceted. However, since then, some additional specimens have been found once again in northern Burma. Since Painite is a relatively hard gem at about the same level as any spinel or tourmaline, it is perfectly suitable for any jewelry design
Taaffeite is another extremely rare gem type. Most of the early finds were previously misclassified as spinel, which it does closely resemble. In fact, taaffeite was first discovered as an already polished and faceted gemstone; Count Edward Charles Richard Taaffe (1898-1967) discovered that one of the spinel gems contained in a parcel he purchased from a Dublin dealer was doubly refractive. Lab testing later confirmed that it was indeed a new species of beryllium, magnesium and aluminum oxide by chemical composition. As of now, taaffeite has only been found in Sri Lanka. Musgravite, another gem that is a polytype (crystallography) of taaffeite, is equally as rare occurring as taaffeite. Taaffite is also the same hardness level as Spinel which makes it perfectly acceptable for any type of jewelry design including rings should one risk wanted to wear one.
Jeremejevite is a very rare gem of aluminum borate mineral composition. It was discovered in Siberia and named after a Russian mineralogist in 1883. Jeremejevite has a hardness rating of 6.5 to 7.5 and its color can range from being colorless to yellow to blue. Recently, some facet-grade quality specimens were discovered in Namibia. Similar to tourmaline, jeremejevite is piezoelectric and can thus carry an electrical charge. Since Jeremejevite is a softer gem, often softer than quartz depending purity, it would not be ideal for any ring jewelry, but could be worn as an exquisite pendant or other accessory. Many times, Jeremejevite is worn in its rough form and not cut or polished like most other gemstones. This may be due to the fact that it is so rare, cutting the stone only loses most of what little material is there in the first place - so by wearing it in its rough state, the more material that can be preserved. Afterall, it is one of the rarest gem types on earth.
Poudretteite is a rare borosilicate first discovered in Quebec, Canada. The discovery was made during the 60's, and the rare gem type was named after the family that operated the quarry of which it was found. Poudretteite is usually pink, purple or colorless and has a hardness of 5 to 6 on mohs scale. Specimens of poudretteite have been discovered in Burma (Myanmar).
Serendibite was first found in Sri Lanka (Ceylon). The name, serendibite, comes from the old Arabic name for Sri Lanka. Only 3 small faceted stones are known to exist, all of which are less than a carat in weight. Two of these gems were purchased by the late, Edward Gubelin.
Some rare gems are used for expensive gemstone jewelry, but the truth is that only the most elite can even possibly afford the loose stones, nevertheless as jewelry. Most rare gemstones are only for collectors, because much of the rarer materials are simply too soft to be worn as jewelry or simply too rare. So rare, that no one in their right mind would want to risk damaging or losing one of the rarest gems in the world!