Mineral Information and Data:

[]NaCa[Mg4Al]Si8O22(OH)2 [CNMNC approved formula]

Named for Howard J. Winch, Geological survey of India. First published in 1906. Species redefined per nomenclature of amphiboles (IMA, 1997).

IMA status : Redefined IMA Approved; 1997 ()
(8th edition) :
  (66) Inosilicate Double-Width Unbranched Chains, W=2
  (66.01) with P=2 amphibole configuration
  (66.01.03b) Group 3, the sodic-calcic amphiboles
(10th edition) :
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C2/m
Unit cell: a = 9.834Å, b = 18.062Å, c = 5.3Å β = 104.449°, Z=2
Crystal Habit: In stout prismatic to acicular crystals, to 4 cm. As blades, fibers, and in rosettes or spherules.
Color: Colorless, cobalt blue to bluish violet; colorless to pale blue in thin section
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 5 - 6
Measured Density: 2.97 - 3.175 g/cm3
Cleavage: Perfect on {110}, intersecting at ~56° and ~124°; partings on {100}, {001}
Tenacity: Brittle
Fracture: Uneven
Polymorphism and Series: Forms a series with ferrowinchite.
Geologic Setting: In schists with low-grade metamorphosed manganese deposits; in metabasalts of the jadeite-glaucophane and amphibolite-eclogite facies; in manganiferous cherts that have undergone blueschist facies metamorphism.
Mineral Association: Calcite, microcline, diopside, plagioclase, apatite, tremolite (Kajlidongri mine, India);
omphacite, garnet, rutile, quartz, actinolite, epidote, albite, titanite, apatite (Margarita Island, Venezuela);
actinolite, glaucophane, albite, quartz (Ward Creek, California, USA)
Comments: Crystals are commonly strongly zoned chemically.


Bluish violet- colored winchite in braunite
Origin: Tivadi, India
Sample size: 5 x 4.6 x 3 cm
Photo: Rob Lavinsky


(zoom-in of above)