] typically found in Japan
, South Africa
, and on Iwagi Island
. Due to its vivid color, it is used primarily in jewelry making.
Potassium 3.80 % K 4.58 % K2O
Sodium 4.47 % Na 6.03 % Na2O
Lithium 2.03 % Li 4.36 % Li2O
Manganese 3.21 % Mn 4.14 % MnO
Aluminum 0.52 % Al 0.99 % Al2O3
Iron 6.52 % Fe 8.38 % FeO
Silicon 32.78 % Si 70.12 % SiO2
Oxygen 46.68 % O
100.00 % 98.60 % = Total Oxide
Usually purple, black, and brown in color, Sugilite forms hexagonal crystals though occurances of them are quite rare, and when found are often massive in size. With a refraction index of 1.60 and a hardness 6 - 6.5, the stone is usually found in aegirine syenite.
The stone has subconchoidal fracturing and cleavage in one direction. It has a Dana class of 63.2.1a.9, in the Milarite - Osumilite subgroup, with Cyclosilicate Condensed Rings. Overall a fairly rare stone, it is highly prized for it's rich purple colors for cabs.
The highest quality pieces are usually translucent and cabbed, thereby being used in jewelry. I find that it is most attractive set with turquoise or other similar stones, and has a similar value to it as well as lapis.
http://webmineral.com/data/Sugilite.shtml - Contains excellent further information on optical and physical properties of the substance.