Hydrated phosphate, fairfieldite group, forms a solid solution with collinsite
Specific gravity: 3.16
Colour: Colourless to greenish grey
Solubility: Very slowly soluble in hydrochloric acid
The type locality is Reaphook Hill, Martins Well, South Flinders Ranges, South Australia, and to date (January 2021) this is the only locality where hillite has been identified. It has been found as doubly terminated euhedral crystals, less than 50 μm long, and as concentric zones up to 200 μm in thickness within zinc-bearing collinsite. Hillite occurs on the prism faces of scholzite, as concentric zones within collinsite, and as clusters of crystals on crusts of collinsite in a small gossan on argillaceous siltstone. Other phosphates in the gossan include tarbuttite, parahopeite, switzerite and phosphophyllite (CM 41.981-988).
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