Sugilite: A Rare Precious Stone

Gem sugilite is a polycrystalline aggregate: a massive gem material that is colored a very attractive purple-violet color, due to the presence of manganese. It is named for Ken-ichi Sugi, the Japanese geologist who discovered it in 1944 on an island in Japan.

Sugilite is a relatively rare pink to purple cyclosilicate mineral with the complex chemical formula KNa₂(Fe³⁺,Mn³⁺,Al)₂Li₃Si₁₂O₃₀. Sugilite crystallizes in the hexagonal system with prismatic crystals. The crystals are rarely found and the form is usually massive. It has a Mohs hardness of 5.5 to 6.5 and a specific gravity of 2.75 to 2.80. It is mostly translucent.

Sugilite: A Rare Precious Stone. 16kg Manganoan Sugilite from Wessels Mine in Northern Cape Province, South Africa
Photo: RDCnet CC

Sugilite occurs in bedded manganese deposits as an aegirine-bearing syenite stock in biotite granite. This uncommon cyclosilicate mineral displays violet to purple-red coloring. Sugilite crystallizes in the hexagonal system with prismatic crystals. Although crystal specimens of sugilite are infrequently discovered, those that have been found they are usually very large.

Sugilite deposits are found in Australia, India, Japan, Canada and South Africa.

Sugilite is popular in jewelry, in thin sections which can be polished or cut into cabochons and mounted in silver or gold in rings, pendants, and earrings. In the 1980s the gem was heavily promoted on home shopping channels and internet auctions sites.

With a Mohs scale hardness of 5-1/2 to 6-1/2, sugilite is somewhat durable. However, be careful wiping dust from sugilite because household dust contains quartz, which may cause scratches. It is recommended to clean sugilite gemstones by using soapy water, rinsing well and drying with a soft cloth. Ultrasonic cleaners and steamers are not recommended. Always remove any jewelry or gemstones before exercising, cleaning or engaging in physical activities such as sports. Store sugilite gemstones away from other gemstones to prevent scratches, wrapped in soft cloth or placed inside a fabric-lined box.

Properties of Sugilite:

Color is purple, brown to yellow, pale pink and even black.
Luster is vitreous to dull or waxy.
Transparency: Crystals are translucent to opaque.
Crystal System is hexagonal; 6/m 2/m 2/m.
Crystal Habits include rare striated prismatic crystals, but specimens are usually massive.
Cleavage is poor in one direction.
Fracture is subconchoidal.
Hardness is 6 - 6.5
Specific Gravity is approximately 2.75 - 2.80 (average)
Streak is brown.
Associated Minerals include pectolite, poudretteite and polylithionite.
Notable Occurrences include the type locality of Iwagi Island, Shikoku, Japan as well as Mont Saint-Hilaire, Quebec, Canada and most importantly, South Africa.
Best Field Indicators are color, hardness, luster, streak and locality.