Sweetite

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]