Sugilite
Last updated: April 2026
A rare cyclosilicate mineral found almost exclusively at the Wessels Mine in the Kalahari Manganese Field, Northern Cape, South Africa. Prized for its vivid purple color — top 'gel' quality is translucent with an intense grape-like purple that commands premium prices.
Sugilite has a specific gravity of 2.76 and a refractive index of 1.607–1.610, with a Mohs hardness of 5.5–6.5. It is uniaxial −.
Physical & Optical Properties
Measured with a polariscope, a refractometer, a hydrostatic balance, a Chelsea filter, a UV torch, a loupe, a darkfield loupe and a spectroscope — step-by-step for each.
Through the refractometer
Drawn from the refractive index above, on a 1.40–1.81 scale. How to take this reading.
Key Differentiators
- Vivid purple to violet color, often with rich grape-juice saturation
- Massive polycrystalline habit — no visible crystal faces or transparency
- Primarily from Wessels Mine, Northern Cape, South Africa
- RI 1.607–1.610 distinguishes from amethyst (1.544) and charoite (1.550–1.559)
- SG 2.74–2.80 — heavier than charoite (2.54–2.68) and fluorite (3.18)
Common Simulants
- Charoite: Charoite has distinctive fibrous swirling texture with orange (tinaksite) and black (aegirine) inclusions; RI 1.550–1.559 (lower); SG 2.54–2.68 (lighter).
- Purple Fluorite: Fluorite is transparent, SG 3.18 (much heavier), perfect octahedral cleavage, RI 1.434 (much lower). Easily distinguished.
- Amethyst: Amethyst is crystalline and transparent/translucent, RI 1.544–1.553 (lower), SG 2.65, birefringence 0.009. Sugilite is massive and opaque.
Treatments
- Wax or Resin Impregnation
- Dyed (lower-quality pale material)
Measurement Guides
Identifying a sugilite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Sugilite is one of the 132 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →