Sugilite
Sugilite is a relatively new mineral discovered within rocks on Iwagi Island in Ehime Prefecture, Japan, and is characterized by its intense purple to reddish-purple hue. After being announced as a new mineral in 1976, the discovery of vivid purple sugilite caused by manganese in the Wessels Mine in South Africa in 1980 made it widely known as a gemstone. Today, almost all gem-quality sugilite found on the market is said to originate from this Wessels Mine.
Sugilite with an impressive deep purple color
Basic Information
| English Name | Sugilite |
|---|---|
| Japanese Name | Sugi-ishi (Sugilite) |
| Chemical Composition | K Na₂(Fe²⁺,Mn²⁺,Al)₂Li₃[Si₁₂O₃₀] |
| Crystal System | Hexagonal (granular aggregates) |
| Hardness | 5.5–6.5 |
| Specific Gravity | Approx. 2.75 |
Origin, History, and Varieties
Following its discovery in Japan, vivid purple sugilite was found in manganese deposits in South Africa, associated with minerals such as braunite, manganite, and psilomelane. The highest-grade quality is specifically called "Imperial Sugilite."
- Wesselsite: Sugilite from the Wessels Mine where the spaces between grains are filled with chalcedony. Internal chalcedony filling is confirmed through gemological testing.
- Matrix Sugilite: Refers to specimens polished while embedded in host rock such as psilomelane or braunite.
- Initially, it was mistakenly announced as Zr-bearing sogdianite, but sugilite itself does not contain Zr.
Treatments, Similar Stones, and Identification
Stones with a coarse structure and noticeable porous areas may undergo impregnation with oil or other substances to stabilize their appearance.
Stones with similar colors or characteristics include spurrite, stichtite, and charoite. Stichtite can be distinguished by its very low hardness of 1.5–2.5, making it much softer than sugilite. Spurrite, famous for occurrences in Fuka, Okayama Prefecture, and New Mexico, USA, effervesces when in contact with hydrochloric acid (HCl), whereas sugilite does not.
Some stones feature patterns of dots, circles, or streaky lines resembling "flowering stone" (kamon-seki), and these are popular as highly decorative loose stones. Note that many stones commonly referred to as "Blue Sugilite" are actually different minerals such as Pectolite (Larimar) or Richterite.
Handling Tips: For expensive Imperial-grade specimens, issues regarding impregnation treatments or confusion with similar stones can arise. It is recommended to choose loose stones or jewelry that come with clear documentation of origin, treatment history, and identification results.