SAPPHIRE ROUGH CRYSTALS

 This is a natural untreated specimen from Sril Lanka (Ceylon). Great specimen

Weight 2.36 cts app

Size 12 x 5 x 5 mm app

Sapphire is one of the two gem varieties of the species corundum. Although blue is the best known hue, the gem occurs in virtually every spectral hue excepting red. Red corundum is a ruby. Sapphire may also be colorless, and it also occurs in the non-spectral shades, gray and black. Yellow and green sapphires have traces of iron that gives them their color. Pink sapphires have a trace of the element chromium and the deeper the color pink the higher their monetary value as long as the color is going toward the red of rubies. Sapphires also occur in shades of orange and brown, and colorless sapphires are sometimes used as diamond substitutes in jewelry. Salmon-color padparadscha sapphires often fetch higher prices than many of even the finest blue sapphires.

Treatments

Some natural sapphires are heated to improve or enhance color. This is usually done by heating the sapphires to temperatures of up to 1800 °C for several hours, or by heating in a nitrogen deficient atmosphere oven for seven days or more. On magnification, the silk due to included rutile needles are often visible. If the needles are unbroken, then the stone was not heated; if the silk is not visible then the stone was heated adequately. If the silk is partially broken, then a process known as low tube heat may have been used. Low tube heat is the process whereby the rough stone is heated to 1300 °C over charcoal for 20 to 30 minutes. This removes grey or brown in the stone and improves color saturation.