apatite, Tanzania, gems

Gübelin and Schmetzer describe a new occurrence of cat’s-eye apatite from the Umba Valley, Tanzania, occurring in yellow, green and reddish-brown colors. A small proportion of the material is clear and transparent, but most specimens contain abundant fine, fibre-like inclusions and are therefore suitable for cabochon cutting. Properly oriented cabochons display a strong, sharply defined cat’s-eye effect. Examination of the inclusions showed that the chatoyancy is produced by numerous minute needles of goethite. The article illustrates the material with four color photographs.