Thulite
Zoisite var. Thulite · Semi-Precious Gemstone / Decorative Stone
Crystal System
Orthorhombic; typically occurs in massive, granular, or fibro-lamellar habits rather than distinct crystals.
Mineral Group
Silicates (Sorosilicates); Epidote group.
Chemical Formula
Ca2Al3(SiO4)3(OH) - with Manganese (Mn) as the chromophore
Formation Process
Metamorphic; typically forms during regional metamorphism of calcium-rich rocks like limestone or marble, often in manganese-rich environments.
About This Crystal
A vibrant pink to rose-red variety of zoisite. It is usually opaque to translucent with a vitreous to pearly luster. The texture is often granular or mottled with white or gray quartz or calcite inclusions.
Physical Characteristics
Color: Pink, rose-red, or reddish-pink. Streak: White. Cleavage: Perfect in one direction (though rarely visible in massive form). Fracture: Uneven to conchoidal. Specific Gravity: 3.10–3.38. Fluorescence: Usually none, though some specimens may show weak orange-red.
Optical Properties
Refractive Index: 1.691–1.700. Birefringence: 0.006–0.018. Pleochroism: Strong (yellow, pink, and colorless/yellowish). Doubly refractive.
Hardness & Durability
Origin Region
Originally discovered in Norway (Telemark); also found in Australia, Namibia, and the United States (North Carolina and Washington). Forms in regional metamorphic environments.
Hardness & Durability
Mohs hardness: 6 to 7. It is relatively tough but can be brittle due to cleavage planes. Suitable for cabochons and carvings but should be protected in rings.
Care & Maintenance
Clean with warm soapy water and a soft cloth. Avoid ultrasonic cleaners and steam cleaners. Sensitive to sudden temperature changes and strong acids. Store separately from harder gemstones like sapphire.
Rarity & Value
Uncommon. High-quality, saturated pink material from Norway is the most valued. Price is generally affordable, mostly sold as cabochons, beads, or decorative carvings. Most material is natural and untreated.
Special Characteristics
Known for its intense pink color caused by manganese replacing calcium in the crystal lattice. Massive varieties often show a distinctive 'mottled' appearace due to mineral intergrowths.
Lore & History
Named after the mythical island of Thule (associated with Norway). Historically used as a decorative stone in Scandinavia. In metaphysical traditions, it is associated with the heart chakra, believed to promote compassion, joy, and emotional healing.