feldspar, gems

Describes light blue to light green gem-quality feldspar from pegmatite dykes near Kioo, Kenya, approximately 13 km east of Sultan Hamud. The material resembles aquamarine in colour and has a vitreous lustre. Optical measurements, X-ray diffraction and electron microprobe analyses identify a sodium-rich plagioclase with a peristerite structure. Reported inclusions comprise distinctive growth irregularities, fingerprint-like patterns containing occasional two-phase inclusions, and vermiculite crystals. The article also outlines the geological setting, associated minerals and mining methods.