Hexagonite

This article is about the mineral. For the extinct mollusc, see Hexagonites.
Hexagonite
General
Category mineral variety of tremolite
Formula
(repeating unit)		 Ca2Mg5 (Si8O22) (OH)2
Space group monoclinic – prismatic
Identification
Color red 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 hardness 5.0–6.0
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.

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. Pink, lilac, and purple are the most common colors.[1] Transparent examples with nice coloration are most prized. Hexagonite can also display a good Cat's eye effect. 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: Ca2Mg5 (Si8O22) (OH)2.[3]

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

Found

Today, the mineral is found primarily in the Balmat-Edwards zinc district of St. Lawrence County, New York, United States.[4] Although very rare, it can be found elsewhere in other locations worldwide.

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


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