There are roughly 200 varieties of natural gemstone known in the world today. Alongside the world’s precious gems (diamond, ruby, sapphire, and emerald) are numerous semi-precious stones, some of which are so incredibly rare that their value outstrips many of the world’s most valuable precious gems. Here are a few of the rarest from around the world.
- Tanzanite – found only in Tanzania
Tanzanite is a beautiful blue variety of the mineral zoisite, and is so named because it is only found in a small area near the foot of Mount Kilimanjaro in Tanzania. The stone was not discovered in commercial quantities until the 1960s and since then its popularity has grown tremendously, thanks largely to the efforts of Tiffany & Co. Heat-treating tanzanite at very high temperatures can improve the blue coloration, so most gems on the market have been treated in this way, but any tanzanite that has not been heat-treated and has a strong blue colour naturally will be of a much higher value. Because it is only found in one small location, the value of tanzanite looks likely to soar over time; once those mines have been emptied there will be no new stones coming onto the market—unless a new source is found.
- Black opal – the darker the better
Opals are usually a creamy-white colour and are made special by the rainbow-coloured inclusions that reflect the light as the stone is moved. Black opals are much rarer, because almost all of them are found in mines in the Lightning Ridge area of New South Wales in Australia. The darker their background colour and brighter the inclusions, the more valuable the stone. One of the most valuable black opals of all time is the “Aurora Australis,” which was uncovered in Lightning Ridge in 1938. The 180-carat opal is especially admired due to its large size and intense harlequin coloration; in 2005 it was valued at AUS $1,000,000 (USA $763,000)