Sweetite

General
Category| Hydroxide mineral
Formula
(repeating unit)| Zn(OH)2
Strunz classification| 4.FA.10
Crystal system| Tetragonal
Unknown space group
Crystal class| Trapezohedral (422)
H-M symbol: (422)
Space group| P41212 (no. 92) or P43212 (no. 96)
Unit cell| a = 8.22, c = 14.34 [Å]
V = 968.93 Å3; Z = 20
Identification
Formula mass| 99.40 g/mol
Color| Colorless, white
Crystal habit| Bipyramidal
Cleavage| None
Fracture| Irregular
Mohs scale hardness| 3
|re|er}}| 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).[6] 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.[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.[1]

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

## References

1. ↑ 1.0 1.1 1.2 Webmineral data
2. ↑ Mindat.org
3. ↑ Mineral Atlas
4. ↑ 4.0 4.1 4.2 Handbook of Mineralogy
5. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
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.

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