Thulite
Last updated: April 2026
Thulite is a manganese-bearing pink variety of zoisite used primarily in ornamental work and cabochons; it is opaque to translucent with a characteristic rose-pink color from Mn substitution in the zoisite structure.
Thulite has a specific gravity of 3.20 and a refractive index of 1.691–1.704, with a Mohs hardness of 6.0–7.0. It is biaxial +.
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.
Related: Zoisite Varieties
Key Differentiators
- Opaque to translucent pink zoisite — massive habit, typically cabochon or ornamental
- Higher RI (1.691–1.704) and SG (~3.20) than rose quartz (RI 1.544, SG 2.65) — easy separation by refractometer
- Softer than rhodonite (H 5.5–6.5) with lower RI (rhodonite RI 1.716–1.752, SG 3.57–3.76)
- No black MnO veining (unlike rhodonite which shows diagnostic black vein network)
- Named for Thule (ancient name for Norway) — type locality Leksvik, Norway; also Tanzania and North Carolina
Common Simulants
- Rhodonite: Rhodonite: RI 1.716–1.752, SG 3.57–3.76 (higher than thulite); black MnO dendritic veining; triclinic crystal system.
- Rose Quartz: Rose quartz: RI 1.544–1.553, SG 2.65 — much lower RI and SG than thulite; trigonal, uniaxial DR; translucent milky pink without zoisite texture.
- Rhodochrosite: Rhodochrosite: much softer (H 3.5–4), RI 1.600–1.816 (extreme birefringence), effervesces with dilute HCl; shows concentric white-pink banding.
- Pink Aragonite / Pink Calcite: Carbonate mineral: H ~3, effervesces with HCl; RI 1.530–1.685 range depending on variety; much lower hardness and SG.
Treatments
- Wax / Resin Impregnation (ornamental surface treatment)
Measurement Guides
Identifying a thulite? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Thulite 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 →