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Category Hydroxide mineral
(repeating unit)
Strunz classification 4.FA.10
Crystal system Tetragonal
Unknown space group
Crystal class Trapezohedral (422)
H-M symbol: (422)
Unit cell a = 8.22, c = 14.34 [Å]
V = 968.93 Å³; Z = 20
Formula mass 99.40 g/mol
Color Colorless, white
Crystal habit Bipyramidal
Cleavage None
Fracture Irregular
Mohs scale hardness 3
Luster Vitreous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.33
Optical properties uniaxial (-)
Refractive index nω = 1.635 nε = 1.628
Birefringence 0.007
References [1][2][3][4]

Sweetite has a general formula of Zn(OH)2.[1] The name is given after a curator of mineral department of The British Museum, Jessie May Sweet (1901–1979).[5] It occurs in an oxidized vein in limestone bedrock with galena, ashoverite, wülfingite, anglesite, cerussite, hydrocerussite, litharge, fluorite, palygorskite and calcite.[4]

Sweetite is tetragonal, which means crystallographically it contains one axis of unequal length and two axes of equal length. The angles between three of the axes are all 90°. It belongs to the space group 4/m. Some crystals show evidence of a basal plane and a few are tabular.[6] In terms of its optical properties, sweetite has two indices of refraction, 1.635 along the ordinary ray and 1.628 along the extraordinary ray.[7] The index of refraction is the velocity of light in a vacuum divided by the velocity of light in medium. It also has the birefringence of 0.007.[8] The birefringence means the decomposition of light into two rays when passing through a mineral. Sweetite is 1.64 - 1.65 in relief, which is medium to high in intensity and means a measure of the relative difference between the index of refraction of a mineral and its surrounding medium.[1]

Sweetite is mostly found from a limestone quarry 200–300 m northwest of Milltown, near Ashover, Derbyshire, England.[4]


  1. ^ a b c Webmineral data
  2. ^ Mindat.org
  3. ^ Mineral Atlas
  4. ^ a b c Handbook of Mineralogy
  5. ^ Ralph, Jolyon. "Sweetite" Mindat.org. 2010. 17 Sep 2010
  6. ^ Clark, A.M., Fejer, E.E., Couper, A.G., and Jones G.C. (1984) Sweetite, a new mineral from Derbyshire. Mineralogical Magazine, 48, 267-269.
  7. ^ Ralph, Jolyon. "Sweetite" Mindat.org. 2010. 7 Nov 2010
  8. ^ "Sweetite" (http://webmineral.com/data/Sweetite.shtml). Mineral Data. http://webmineral.com/data/Sweetite.shtml. Retrieved 7 November 2010.