Tarbuttite

Tarbuttite is a rare phosphate mineral with formula Zn2(PO4)(OH). It was discovered in 1907 in what is now Zambia and named for Percy Tarbutt.
Description and habit
Tarbuttite is white, yellow, red, green, brown, or colorless; in transmitted light it is colorless. Traces of copper cause green coloring, while iron hydroxides cause the other colors. Colorless crystals tend to be transparent while colored specimens have varying degrees of transparency.
The mineral occurs as equant to short prismatic crystals up to 2 centimetres (0.79 in), in sheaf-like or saddle-shaped aggregates, or as crusts. Individual crystals are commonly rounded and striated.
Structure
Zinc ions are surrounded by oxygen in a nearly perfect trigonal bipyramid and phosphate groups are tetrahedral. The crystal structure consists of zig-zag chains of Zn1 polyhedra linked by phosphate groups and pairs of Zn2 polyhedra...