Tremolite Value, Price, and Jewelry Information

TREMOLITE: Hexagonite, Balmite, New York (~1, crystal ~ 1 inch long). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Tremolite

Tremolite Value

Highest values go to faceted gems, particularly Hexagonite and chrome Tremolite, and strong cats eyes.

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Tremolite Information

Data Value
Name Tremolite
Varieties Chrome-Tremolite, Hexagonite
Colors White, colorless, gray, pale greenish, pink, brown.
Hardness 5-6
Wearability Good to Poor
Wearability Notes Good (aggregates); Poor (crystals)
Fracture Uneven
Cleavage Good 2 directions
Stone Sizes Small colorless and transparent tremolite crystals are very rare, and cut gems are true collector items. The largest of these is in the 5-10 carat range. Larger crystals exist but are usually badly fractured. Hexagonite is known in facetable material only from New York and these pieces yield gems to only about carat. Chrome tremolite is also very rare and cut gems are tiny. Catseye hexagonites have also been cut. Private Collection: 1.21 (medium purple, New York).  National Museums of Canada (Ottawa, Ontario): 1.39 (deep purple, New York); 4.55 (dark blue catseye, Ontario); 12.55 (dark brown catseye, Ontario).
Heat Sensitivity yes
Formula Ca3Mg5Si8O22(OH)2 + Fe.
Crystallography Monoclinic. Crystals prismatic or bladed; fibrous, massive, granular.
Refractive Index 1.560-1.643
Birefringence 0.017-0.027; hexagonite 0.019-0.028.
Luminescence Tremolite not diagnostic. Actinolite inert. Hexagonite shows orange, medium pink to pinkish red fluorescence in LW, SW. Also, medium greenish white in SW (Lee, Massachusetts) and dull yellowish in LW.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Absorption Spectrum Not diagnostic. Actinolite: faint line at 5030. Some tremolite shows a line at 4370 typical of jadeite. Chromiferous material may display chromium spectrum.
Pleochroism Hexagonite: bluish-red/deep rose/deep red-violet. Tanzanian green crystals: light yellowish green/light green/green.
Optics a = 1.560-1.562; β = 1.613; γ = 1.624-1.643. Biaxial (-), 2V= 81°. Note: Tanzania, green crystals: 1.608-1.631.
Optic Sign Biaxial -
Luster Vitreous.
Polish Luster Vitreous.
Fracture Luster Vitreous to dull.
Specific Gravity 2.9-3.2 (catseye gem, Ontario, 2.98; hexagonite, 2.98-3.03).
Transparency Transparent to opaque, actinolite usually translucent.
Phenomena Chatoyancy.

Optics

a =1.560-1.562; β= 1.613; γ=1-624-1.643

Biaxial (-), 2V= 81°.

Note: Tanzania, green crystals: 1.608-1.631, S.G. 3.02.

Occurrence

Tremolite occurs in contact and regionally metamorphosed dolomites, in magnesian limestones, and in ultrabasic rocks.

  • California; Arizona; Utah; Colorado; Connecticut; South Dakota; Massachusetts.
  • Italy; Switzerland; Austria.
  • Fowler, New York: hexagonite, some cuttable; also at Edwards and Balmat, New York.
  • Ontario and Quebec, Canada: gray, green and blue crystals; a chatoyant greenish variety found in Ontario cuts interesting catseye gems.
  • Burma: green catseye gems.
  • Lelatemu,Tanzania: green facetable crystals up to 25mm.
  • Sierra Leone: Cr-rich tremolite, deep green with Cr spectrum displayed.

Comments

It is possible to misidentify tremolite, mistaking it for other amphiboles. Hexagonite is the rarest of the gem varieties of tremolite. If tremolite occurs in very tiny fibrous crystals, densely matted and interlocked, it is then known as nephrite (jade). Material containing more or less parallel fibers is somewhat chatoyant and yields weak catseyes. These are sometimes called catseye jades, but have been tested and are actually tremolite or (if more iron-rich) actinolite.

Name

From the Tremola Valley on the south side of St. Gotthard, Switzerland. Hexagonite was so named because it was thought to be a hexagonal mineral when first described.

Variety Names

 Hexagonite, purple Tremolite

 

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