Hexagonite is the red to pink, lilac to purple manganoan variety of tremolite. A rare amphibole, it can be transparent, translucent, and rarely opaque.

Hexagonite
General
Categorymineral variety of tremolite
Formula
(repeating unit)
Ca2Mg5 (Si8O22) (OH)2
Space groupmonoclinicprismatic
Identification
Colorred to pink, lilac to purple
Crystal habitelongated, bladed crystals, granula
Twinningsimple, multiple
Cleavage[110] perfect; [010] distinct
Fractureuneven
Tenacitybrittle
Mohs scale hardness5.0–6.0
Lustervitreous
Refractive index1.599–1.637 biaxial ( - )
Birefringence0.019–0.028
Pleochroismbluish–red, deep rose, deep red–violet
Dispersionweak, r < v

Properties

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Hexagonite is pleochroic, potentially displaying varying shades of blue, violet, purple, or red.[1] It is also known as "mangan-tremolite", since the manganese imparts the mineral's unique colors.[citation needed] Pink, lilac, and purple are the most common colors.[1] Hexagonite has been successfully faceted.[1]

Chemical formulae and history

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Tremolite was discovered in 1789.[2] Hexagonite, a varietal form of tremolite, has a Mohs hardness of 5.0-6.0.[3] Like tremolite, it is a calcium magnesium silicate hydroxide with the formula: Ca2Mg5 (Si8O22) (OH)2.[3]

The mineral was given the name, hexagonite, because its crystal structure was believed at one time to be hexagonal. Since then, however, it has been found to be monoclinic.[3]

Occurrence

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The mineral is found primarily in the Balmat-Edwards zinc district of Edwards, St. Lawrence County, New York, United States.[4] It was also found in the Czech Republic in the Chýnov caves.[5]

References

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  1. ^ a b c Hexagonite Gemstone Information; Gem Data website; accessed August 2016
  2. ^ Tremolite on Mindat.org
  3. ^ a b c Hexagonite on Mindat.org
  4. ^ Balmat Hexagonite; article; July 27, 2015; Fred Haynes blog; "WCGMC Activity;" accessed Aug 2017
  5. ^ Litochleb J, Sejkora J (2007) Occurrence of tremolite-hexagonite in dolomite marbles in the Chýnov cave (southern Bohemia). Minerál 15: 124-126 (in Czech)