Hydroxylapatite replacing Tarbuttite

specimen number:
2133175

location:
Skorpion Mine, Rosh Pinah, Namibia

description:
Platy crystals of tarbuttite measuring to 0.3 cm in size across the front of matrix and in the process of being replaced by white hydroxylapatite. This is in good condition.

The Skorpion Mine, located near Rosh Pinah in southern Namibia, is a major zinc mining operation developed in the early 21st century to exploit a large, oxidized zinc deposit hosted in sedimentary rocks. Unlike many traditional sulfide based zinc mines, Skorpion processes oxide ore, primarily smithsonite, using a hydrometallurgical method to produce high purity zinc. The deposit formed through the weathering and alteration of earlier sulfide mineralization, resulting in a complex assemblage of secondary minerals. Mining is carried out by open pit methods, and the operation has been an important contributor to Namibia's mining industry and global zinc production.

Pseudomorphs are minerals that have replaced an earlier mineral while preserving the original external crystal form. In the case of hydroxylapatite replacing tarbuttite, this process can sometimes be observed in partial stages, where the original tarbuttite crystal is still present but is gradually being altered and replaced by hydroxylapatite. This occurs when changing chemical conditions make tarbuttite unstable, causing it to dissolve while hydroxylapatite precipitates in its place. During this transition, specimens may show a mixture of both minerals, with the outer shape of the original crystal retained even as the internal composition changes. These partially replaced pseudomorphs are especially interesting because they provide direct evidence of the mineral replacement process in progress.

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