Hexagonite

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Hexagonite
Tremolite-172420.jpg
General
Categorymineral variety of tremolite
Formula Ca 2 Mg 5 (Si 8 O 22) (OH)2
Space group monoclinic – prismatic
Identification
Colorred to pink, lilac to purple
Crystal habit elongated, bladed crystals, granula
Twinning simple, multiple
Cleavage [110] perfect; [010] distinct
Fracture uneven
Tenacity brittle
Mohs scale hardness5.0–6.0
Luster vitreous
Refractive index 1.599–1.637 biaxial ( - )
Birefringence 0.019–0.028
Pleochroism bluish–red, deep rose, deep red–violet
Dispersion weak, r < v

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

Contents

Properties

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

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: Ca 2 Mg 5 (Si 8 O 22) (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

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

  1. 1 2 3 Hexagonite Gemstone Information; Gem Data website; accessed August 2016
  2. ↑ Tremolite on Mindat.org
  3. 1 2 3 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)
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