THE MINERAL SUGILITE

Chemistry: KNa₂Li₃(Fe, Mn, Al)₂Si₁₂O₃₀, Potassium Sodium Lithium Iron Manganese Aluminum Silicate.
Class: Silicates
Subclass: Cyclosilicates
Group: Milarite - Osumilite
Uses: As an ornamental and semi-precious stone used in jewelry and as a mineral specimen.
Specimens

Sugilite is a somewhat obscure mineral named for the Japanese geologist who discovered the first specimens in 1944, Ken-ichi Sugi. It is becoming very popular in the jewelry trade. It does not form well shaped crystals but is usually massive. This is OK, as it is used mostly for ornamental and semiprecious stone purposes. It has a very distinctive opaque purple color when found in its most desirable color shades. The polished stones are mostly opaque with an almost waxy luster and a deep reddish purple color. It has been described as a purple turquoise although there is no relation between the two minerals. Its jewelry uses are becoming widespread and sugilite is being used in jewelry styles with turquoise, malachite and coral. Some sugilite has been cut into gemstones, but these are very rare.

The primary structural unit of sugilite is a most unusual double ring, with a formula of Si₁₂O₃₀. Normal rings of cyclosilicates are composed of six silicate tetrahedrons; Si₆O₁₈. The double ring is made of two normal rings that are linked together by sharing six oxygens, one from each tetrahedron in each six membered ring (notice the loss of six oxygens in the double ring formula). The structure is analogous to the dual wheels of a tractor trailer and is shared by other members of the Milarite - Osumilite Group.

PHYSICAL CHARACTERISTICS:

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.

Amethyst Galleries'
Mineral Gallery
MINERALS

Birthstones
Gemstones
By Name
Framed
Unframed
By Class: Carbonates; Elements; Halides; Oxides; Phosphates; Silicates; Sulfates; Sulfides
Fluorescent Minerals
Properties
Rocks
Search
Books

SUGILITE specimens:
(hover for more info)

SUGILITE specimen sug-1
$ 178.00

Dims: 3.3 x 2.6 x 1.6" (8.4 x 6.7 x 4.0 cm)

Wt: 10.3 oz. (292 g)

unknown

A chunk of massive Sugilite makes up this cabinet specimen. The material shows no evidence of crystal form or structure and has rough, uneven surfaces and a dull, matte luster. Its color ranges from a beautiful pale-to-deep magenta, with the deeper color running in streaks into the more common, lighter material. A small amount of a deep, red, brown material is attached to the piece- it almost looks like some sort of agate or jasper.

sug-1 ($178.00)

unknown

SUGILITE specimen sug-2
$ 35.00

Dims: 2.2 x 1.6 x 0.8" (5.5 x 4.2 x 2.0 cm)

Wt: 1.7 oz. (49 g)

unknown

This hand specimen consists of a shapeless chunk of massive Sugilite. It shows no crystal form whatsoever, and thus is not appreciably damaged. The material has a dull luster and the obligatory violet color, and shows a dim translucence along some edges. There is no host rock present.

sug-2 ($ 35.00)

unknown

SUGILITE specimen sug-4
$ 28.00

Dims: 2.8 x 1.1 x 0.9" (7.2 x 2.7 x 2.3 cm)

Wt: 1.2 oz. (35 g)

unknown (likely South Africa)

This hand specimen consists of a chunk of massive Sugilite. It shows no evidence of crystal form and does not appear to be freshly damaged, as its surface is quite dusty and dirty. It has the standard pale violet/lavender color and dull luster of its specie, and is opaque. A thin crust of white material rests on one spot, but there is no other material present.

sug-4 ($ 28.00)

unknown (likely South Africa)

SUGILITE specimen sug-3
$ 29.00

Dims: 1.9 x 1.7 x 0.9" (4.8 x 4.3 x 2.3 cm)

Wt: 1.6 oz. (45 g)

unknown

This small Sugilite piece consists basically of a rough, shapeless chunk of massive material. It has the standard pinkish-violet coloration and dull luster of its specie, and is completely opaque. A few veins of a dark gray or black material extend through it, and there is no host rock present.

sug-3 ($ 29.00)

unknown