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Hexagonite  (variety of Tremolite)
Current inventory:  1 gem
 

Chemistry:  Ca₂Mg₅(Si₈O₂₂)(OH)₂

Discovered in 1789 (Tremolite);   IMA status: Hexagonite: Not Valid; Tremolite: Valid
Hexagonite was named for being a hexagonal form of Tremolite but was later shown to be monoclinic. The name Hexagonite has been rejected by the IMA. Tremolite was named by J.G.A. Höpfner for the Tremola Valley (Val Tremola), Central St. Gotthard Massif, Switzerland where the type material was originally thought to be found.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/F.10-10

Nickel-Strunz 10th Ed. ID:

9.DE.10

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Amphibole group;
Forms a series with Actinolite;
Forms a series with Ferro-Actinolite;
Forms a series with Parvo-manganotremolite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Elongated, stout prismatic, bladed crystals, fibrous, granula, columnar aggregates

Twinning:

Tremolite: Simple or multiple: common parallel to [100], rarely parallel to [001]

Physical Properties

Cleavage:

[110] Perfect , [010] Distinct

Fracture:

Uneven

Tenacity:

Brittle

Hardness (Mohs):

5.0 - 6.0

Density:

2.90 - 3.20 (g/cm³)

Luminescence:

Orange, medium pink to pinkish red fluorescence in LW and SW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Pale Lilac, deep Rose, deep Red-Violet, Purplish

Transparency:

Transparent, Translucent

Luster:

Vitreous

Refractive Index:

1.599 - 1.637  Biaxial ( - )

Birefringence:

0.019 - 0.028

Dispersion:

Weak; r < v

Pleochroism:

Bluish-Red/deep Rose/deep Red-Violet

Occurances

Geological Setting:

Contact metamorphism of Ca-Mg siliceous sediments, regional greenschist metamorphism of ultramafic rocks or magnesium carbonate rocks.

Common Associations:

Calcite, Dolomite, Calcian Garnet, Wollastonite, Talc, Diopside, Forsterite, Cummingtonite, Magnesio-Cummingtonite, Riebeckite, Winchite

Type Locality:

Edwards, Balmat-Edwards Zinc District, St Lawrence County, New York, USA

Year Discovered:

1789 (Tremolite)

View mineral photos:

Hexagonite Mineral Photos and Locations

More Information

Mindat.org (Hexagonite)
Mindat.org (Tremolite)
Webmineral.com (Tremolite)

Hexagonite is the rarest of the gem varieties of Tremolite. It is the Manganoan variety of Tremolite distinguished by its pale lilac to purplish color. Tremolite is a member of the Amphibol mineral group that also includes Actinolite, Jade and Nephrite.

Hexagonite is found only in New York, USA in four locations: Edwards, Fowler and Talcville in St. Lawrence County; and Harrisville in Lewis County.
 

  
Hexagonite gems for sale: