The rarest gems are not always the most beautiful or impressive. However, they may be the most expensive, since rarity often drives up price. These are some of the rarest gemstones in the world.
Intensely blue Benitoite is the state gem of California. It was first found in San Benito County, at the headwaters of Clear Creek. It forms distinctive flat crystals like triangles with their points snipped off, which might be taken for sapphire. However, Benitoite is far rarer than sapphire.
According to an article in the fall 1997 edition of Gems and Gemology, California Benitoite was formed by the alteration of blueschist by hydrothermal fluids derived from the metamorphism of serpentinite. Serpentinite is very common in California; it is the state rock. However, when the serpentinite at Clear Creek was altered by repeated tectonic events, besides creating Benitoite, it produced short fiber asbestos, which still floats free in the area. Clear Creek is therefore often closed to protect the public from inhaling asbestos fibers.
Other relatively rare minerals often found with Benitoite include jadeite, melanite garnet, and plasma agate. Lovely Benitoite specimens form on white natrolite veins, sometimes with distinctive sprinklings of small sparkling amber-colored crystals of joaquinite.
Benitoite has since been found in Arkansas and Japan, but the few gem quality stones all come from one mine in a deadly area of California. Benitoite is far more rare than the diamond.
Diamonds are not breathtakingly uncommon, whatever impression advertising may leave. Worldwide, mines produce twelve metric tons of gem quality material each year. Natural red diamond, however, is among the rarest of stones. At the most, 35 faceted naturally red diamonds are known, and most of them are under a carat in weight. Pink diamonds are almost as rare, and some owners like to consider their pink stones to be red. Some true red diamonds have sold for one million dollars a carat or more.
Diamonds are built of a lattice of carbon. This rigid structure makes them in some senses the hardest natural rocks known. Some colored diamonds have impurities in the carbon that gives them their color. In red diamonds however, there are no impurities. The carbon lattice was actually deformed as the diamond was created, and this deformity alters light in a way that creates the beautiful color of a red diamond.
Another red stone is perhaps not so beautiful, but it is nearly as rare. Painite was once considered the rarest gem in the world, but new deposits have since been found in Burma. Painite colors vary from muddy red brown to red orange. Before 2005, most Painite specimens were in museums or at schools, but small quantities are now becoming available to the public.
Gem dealer Arthur Pain discovered the gem in Burma in the 1950s, in a storied area where many precious gems are found, Mogok. Rubies, sapphires, moonstones, lapis and other stones of legendary quality come from the area. However, conditions in the region are said to be inhumane. The laborious work of mining or panning for stones is all done by hand, and workers are poorly compensated. In this undeveloped area, it is not surprising that new deposits of Painite went unexploited for so long.
Red beryl is another extremely rare stone. Most comes from the Utah desert, where it formed in shrinkage cracks in volcanic lava. Beryllium vapors rose up from the lava as surface waters seeped down. These, combined with silica, feldspar, and iron and manganese oxides to form bright raspberry-colored red beryl. The only known deposit of large gem quality stones come from a mine in the WahWah Mountains of Utah. The color is believed to derive from manganese ions in material that would otherwise be colorless.
Red beryl is also known as bixbite and red emerald.
Some other varieties of beryl include emerald, which is tinted green by chromium or vanadium; aquamarine, tinted blue or turquoise by iron; and Morganite, which comes in a lovely range of pinks and peaches which are also also caused by manganese.
Ammolite is a remarkable stone that somewhat resembles vivid opal. It is the fossilized remains of prehistoric ammonites, extinct relatives of the modern squid. Therefore, it is considered a biogenic gem, like pearls and amber, which are also products of life processes.
Ammolite is the official gemstone of the province of Alberta, where it is dug out of the high slopes of the Rocky Mountains. Its shiny iridescence sometimes occurs in a mosaic pattern referred to as dragon skin. It is composed mostly of aragonite, the same material the forms the nacre in pearls, but the color in shimmering Ammolite is more varied, iridescent, and vivid.
Black opal is vivid enough, however. Its mysterious coruscating patches are caused by the optical effects of spheres of hydrated silica. They are stacked closely in the structure of the stone, and form a diffraction grating that breaks light into what is called the opal’s play of color.
Opal is mined in the desert of Australia, where people sometimes live in dug out houses underground to avoid the suffocating heat.
The vast majority of the world’s opals come from Australia’s desert, and the vast majority of that is light or crystal opal. Perhaps 8 percent of all opals mined are black. Not all black opal actually has a black background though. It ranges from blue-gray to black, and would be more properly described as dark opal. It is a stone that charms anyone lucky enough to own it.
These are only some of the rarest gemstones. Some are so rare and valuable that few will ever see one. Some rare gems, such as Painite perhaps, are not attractive but merely valuable. On the other hand, some stones that could almost be described as commonplace are beautiful beyond all describing, especially if they come from a loved one.