Riebeckite

Introduction: Named after the German explorer and rock collector, Emil Riebeck. A German chemist named them 'blau-eisenstein' or blue ironstone before being renamed crocidolite shortly afterwards. This mineral becomes brown and brittle after weathering and the silicification of its weathered fibres forms 'tiger's eye', a quartz variety.

Distribution: Found on farm Groot Aub 267 in the Rehoboth District.

Composition: Silicate.

Crystal system: Monoclinic.

Lustre: Vitreous, silky.

Streak: Blue-grey.

Hardness: 5.