Thulite

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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

RI Range1.691–1.704

SG Range3.10–3.38

SG Typical3.20

Hardness (Mohs)6–7

Crystal SystemOrthorhombic

Optic CharacterDR Biaxial (+)

Birefringence0.009

Dispersion0.012

Fluorescence LWInert

Fluorescence SWInert

Chelsea FilterInert

PleochroismWeak

ColorsRed Pink

SpeciesZoisite

VarietyThulite (Manganese-Bearing Pink Zoisite)

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)

Price Context

Natural — low ($/ct)$5

Natural — high ($/ct)$30

NotePer carat equivalent; primarily ornamental value; carved pieces and fine cabochons command modest premiums; most material is tumbled or decorative

Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.

Measurement Guides

Identifying a thulite? GemID walks through these tests in order — RI, SG, fluorescence, and more.

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Studying for the GIA, FGA, or FEEG practical? Thulite is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.

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