Sweetite

Sweetite
General
CategoryHydroxide mineral
Formula
(repeating unit)		Zn(OH)2
IMA symbolSw[1]
Strunz classification4.FA.10
Crystal systemTetragonal
Unknown space group
Crystal classTrapezohedral (422)
H-M symbol: (422)
Space groupP41212 (no. 92) or P43212 (no. 96)
Unit cella = 8.22, c = 14.34 [Å]
V = 968.93 Å3; Z = 20
Identification
Formula mass99.40 g/mol
ColorColorless, white
Crystal habitBipyramidal
CleavageNone
FractureIrregular
Mohs scale hardness3
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.33
Optical propertiesUniaxial (−)
Refractive indexnω = 1.635 nε = 1.628
Birefringence0.007
References[2][3][4][5]

Sweetite has a general formula of Zn(OH)2.[2] The name is given after a curator of mineral department of the British Museum, Jessie May Sweet (1901–1979).[6] It occurs in an oxidized vein in limestone bedrock with galena, ashoverite, wülfingite, anglesite, cerussite, hydrocerussite, litharge, fluorite, palygorskite and calcite.[5]

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.[7] 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.[8] The index of refraction is the velocity of light in vacuum divided by the velocity of light in medium. It also has the birefringence of 0.007.[9] 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.[2]

Sweetite is mostly found from a limestone quarry 200–300 m northwest of Milltown, near Ashover, Derbyshire, England.[5]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Webmineral data
  3. ^ Mindat.org
  4. ^ Mineral Atlas
  5. ^ a b c Handbook of Mineralogy
  6. ^ Ralph, Jolyon. "Sweetite" Mindat.org. 2010. 17 Sep 2010
  7. ^ 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.
  8. ^ Ralph, Jolyon. "Sweetite" Mindat.org. 2010. 7 Nov 2010
  9. ^ "Sweetite" (http://webmineral.com/data/Sweetite.shtml). Mineral Data. http://webmineral.com/data/Sweetite.shtml. Retrieved 7 November 2010.