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May-June 2017

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Connoisseur's Choice: Leiteite, Tsumeb Mine, Tsumeb, Namibia

Leiteite, ZnAs23+O4, is a micaceous monoclinic zinc arsenite mineral, but unlike mica, it is not brittle but flexible and sectile (Anthony et al. 2000). It is white and cream-colored to pale brown, with some of the first-found specimens exhibiting a pale pink tinge. It is translucent to transparent, and some crystals are actually gemmy. Crystals and cleavage fragments have a highly pearly luster. Cleavage is perfect on {100}, which has allowed some specimens to be cleaved into smaller sections and sold off individually. Gebhard (1999) states that cleavable masses to 17 cm have been collected. Leiteite is a relatively soft mineral, with a hardness of 1.5–2. Crystals have pyramidal terminations. The featured specimen (fig. 1) exhibits the mineral's strongly micaceous habit and is one of the largest known. 

 

Dr. Bruce Cairncross, a consulting editor of Rocks & Minerals, is a professor of geology at the University of Johannesburg

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