Summary: Specimens of tavistockite fall into two groups: true tavistockite from the George and Charlotte mine, Tavistock, Devon, and wavellite from the Stenna Gwyn mine, St. Austell, Cornwall. Both were sold as tavistockite by the discoverer, Richard Talling.
Tavistockite proper is a fluorapatite, as shown by optical and X-ray examination, and the alumina and water in the original analysis are certainly derived from kaolinite with which the apatite is intimately associated.
The published optical properties attributed to tavistockite were determined by E. S. Larsen on Stenna Gwyn material, and are those of wavellite.
Re-examination of a portion of Buttgenbach's type bialite, which he related to tavistockite on optical grounds, shows it to be wavellite.