Saturday, 15 April 2017

Kyanite from Nepal

Kyanite is composed of aluminum silicate; the same as andalusite and sillimanite. Kyanite has a different crystal structure (triclinic) and thus exhibits different physical properties. One of the unusual properties of kyanite is that it has a variable hardness - it is soft when cut parallel to the long axis of the crystal, with a hardness of only 4 to 4.5 on the Mohs scale. But it has a hardness of about 6.5 when cut perpendicular to the long axis. Kyanite has a vitreous to pearly luster. Generally kyanite gems are not found in large sizes
Blue kyanite has long been used as a sapphire imitation. Bright blue kyanite from Nepal might be mistaken for sapphire, but they are easily identified by their different inclusions and optical values. Recent finds of very high quality kyanite in Nepal are changing perceptions of this gem.

Daha is in Jajarkot District in the Bheri Zone of Mid-Western Nepal. Four small-scale kyanite mines are currently in operation in Daha and Suneri in Jajarkot, and Barah in Aachham District. Production is very limited. High quality inky blue kyanite crystals are cut for gems.
Until recently, it was believed that kyanite always formed in shades of blue.

But orange kyanite has now been discovered in Tanzania. The orange color is derived from trace amounts of manganese in the crystals. Kyanite’s name does reflect the more common blue color, and is derived from the Greek word kuanos, which translates to “deep blue.”