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Willemite was discovered in 1830 and named after William I, King of the Netherlands. This stone has remarkable luminescent properties. Some specimens glow under an ultraviolet source and continue to glow after the UV light has been removed, a phenomenon called phosphorescence. Specimens that are faceted make beautiful gemstones in blue, yellow, green and brown colors.

Willemite Polished
Willemite Classification
Common Name Willemite
Species Willemite
Willemite Optical Properties
Transparency Transparent - Opaque
Dispersion Strength: Weak Fire
Refractive Index 1.690-1.723
Birefringence 0.028-0.033
Optic Character Uniaxial
Optic Sign Positive
Polariscope Reaction Aggregate (AGG), Doubly Refractive (DR)
Fluorescence SWUV: Strong green
LWUV: Weak to strong greenish yellow to green
Pleochroism Unobservable
Willemite Characteristic Physical Properties
Hardness 5.5
Streak White
Specific Gravity 3.890-4.180
Toughness Poor
Luster Resinous
Fracture Conchoidal, Uneven
Cleavage Poor, in two directions
Willemite Chemistry & Crystallography
Chemical Name zinc silicate
Chemical Formula Zn2SiO4
Crystal System Trigonal
Chemistry Classification Silicate

Willemite Colors

  • Colorless Willemite Colorless
  • Red Willemite Red
  • Green Willemite Green
  • Yellow Willemite Yellow
  • Brown Willemite Brown
  • Gray Willemite Gray
  • White Willemite White
  • Blue Willemite Blue

Countries of Origin

United States of America (the)

Sisk Gemology Reference

Showcasing 200 gemstones in over 1,000 pages and accompanied by more than 2,000 photos, The Sisk Gemology Reference is a must-have in every collector’s library. Each comprehensive, three-volume set features state-of-the-art photography, detailed illustrations, and scientifically precise descriptions to create an entrancing experience for gemstone amateurs and afficionados alike.

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Tim Matthews


Tim Matthews

Tim Matthews is President and Chief Executive Officer of Jewelry Television® (JTV), as well as a member of the company's Board of Directors. He oversees and leads all aspects of the company's powerful omni-digital retail platform that uniquely specializes in fine jewelry and gemstones. His passion for business and gemstones has led him to become a recognized expert in the field of gemology. He is a life member of the Gemmological Association of Great Britain (Gem-A) and has earned Gem-A's highest degrees, the Gemmology (FGA) and Diamond (DGA) diplomas. He is also a Graduate Gemologist (GG) of the Gemological Institute of America (GIA) and has also completed GIA's Graduate Diplomas in Diamonds, Colored Stones and Pearls. Under his leadership, JTV has become the leader in the sourcing and selling of color gemstones and jewelry.

This page was created on June 27, 2014.

This page was last edited on October 24, 2019.