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Sugilite
Current inventory:  0 gems
 

Chemistry:  KNa₂(Fe³⁺Mn³⁺Al)₂Li₃Si₁₂O₃₀ 
[Potassium Sodium Lithium Iron Manganese Aluminum Silicate]

Discovered in 1944;   IMA status: Valid (IMA approved 1976).
Sugilite is named after Ken-ichi Sugi (1901-1948), Japanese petrologist who discovered it.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/E.22-110

Nickel-Strunz 10th Ed. ID:

9.CM.05

9 : SILICATES (Germanates)
C : Cyclosilicates
M : [Si₆O₁₈]₁₂- 6-membered double rings (sechser-Doppelringe)

Related to:

Osumilite Group. Millarite - Osumilite Series.

Crystal Data

Crystallography:

Hexagonal - Dihexagonal Dipyramidal

Crystal Habit:

Crystals prismatic, to 2 cm, rare. Commonly in interlocking aggregates of subhedral grains, compact to massive.

Twinning:

None

Physical Properties

Cleavage:

[0001] Indistinct/Poor

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Hardness (Mohs):

6.0 - 6.5

Density:

2.74 - 2.79 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 54.07 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Light Brownish Yellow, Lavender, intense Reddish Violet, bright Magenta, Purplish, dark Rose Red

Transparency:

Translucent to Transparent

Luster:

Vitreous

Refractive Index:

1.595 - 1.611  Uniaxial ( - )

Birefringence:

0.0030

Dispersion:

n/a

Pleochroism:

Weak

Occurances

Geological Setting:

In an aegirine-bearing syenite stock in biotite granite (Iwagi Islet, Japan); in bedded manganese deposits (near Kuruman, South Africa).

Common Associations:

Aegirine, Albite, Allanite, Andradite, Apatite, Pectolite, Titanite, Zircon, (Iwagi Islet, Japan)

Common Impurities:

Ti, H₂O

Type Locality:

Iwagi Island, Inland Sea (Setonaikai), Ehime Prefecture, Japan

Year Discovered:

1944; IMA approved 1976

View mineral photos:

Sugilite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Sugilite was originally discovered in 1944 by Japanese geologist Ken-ichi Sugi on Iwagi Island, Japan as very tiny yellowish crystals. It wasn't until 1975, when a thin seam of purplish Sugilite was found in a core sample in the Kuruman manganese fields of South Africa. In 1979 a huge mass, as much as 10-12 tons, of Sugilite was discovered at a depth of 3,200 feet at this location. Only half of this material had the fine grape jelly color that is highly desired. Of this, a tiny percentage (maybe 0.1%) is translucent. Some transparent Sugilite has been cut into gems, but these are very rare. Sugilite has become very popular in the jewelry trade as cabochons and carvings. It has been described as a purple Turquoise although there is no relation between the two minerals.

Sugilite is found in just a few locations worldwide including Liguria, and Tuscany Italy; Iwagi Island, Japan (Type Location); Wessels Mine, Hotazel, Kalahari manganese fields, Northern Cape Province, South Africa.
 

  
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