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The Umba sapphire is a unique type of sapphire discovered in 1962 in the Gerevi Hills, north of the Umba River in the Umba Valley of Mkinga District of Tanga Region in Tanzania. Umba sapphires exhibit coloration not common to sapphires found in other parts of the world, and are recovered from the alluvial deposits of the Umba River.
Intergem rocked the gem trade by marketing the Yogo as the world's only guaranteed untreated sapphire. By 1982, the practice of routinely heat treating gems had become a major issue in the industry. [78] At the time, 95 percent of all the world's sapphires were being heated to enhance their natural color.
Synthetic sapphire—also referred to as sapphire glass—is commonly used for small windows, because it is both highly transparent to wavelengths of light between 150 nm and 5500 nm (the visible spectrum extends about 380 nm to 750 nm [57]), and extraordinarily scratch-resistant. [58] [59] The key benefits of sapphire windows are:
The mineralogy of the gem deposits varies widely with, among others, corundum (sapphire, ruby), chrysoberyl, beryl, spinel, topaz, zircon, tourmaline, garnet being common. [2] Residual deposits are mainly found in flood plains of rivers and streams. The metamorphic types of gems constitute 90% of the gem deposits in Sri Lanka.
The deposit remains open along strike and to depth. The resource is National Instrument 43–101 compliant and is the first coloured gemstone resource ever to be published under these laws. True North Gems has initiated a socio-economic impact assessment in anticipation of a commercial ruby mining operation.
Ruspoli Sapphire: 136.9 carats (27.38 g) [11] Stuart Sapphire: Sri Lanka 104 carats (20.8 g) Blue Tower of London [12] Bismarck Sapphire: Myanmar: 98.56 carats (19.712 g) Table Blue National Museum of Natural History, Washington [13] James J. Hill Sapphire: 22.66 carats (4.532 g) Cornflower National Museum of Natural History, Washington [14]
The Star of India is a 563.35-carat (112.67 g) star sapphire, one of the largest such gems in the world. [1] [a] It is almost flawless and is unusual in that it has stars on both sides of the stone. The greyish-blue gem was mined in Sri Lanka [3] and is housed in the American Museum of Natural History in New York City.
The mineral industry of Colombia is large and diverse; the country occupies the first place in mining areas per surface area in the world. In pre-Columbian times, mining of gold, silver, copper, emeralds, salt, coal and other minerals was already widespread.