Opal from selected localities.
UK | |
| Goley, P. and Williams R. (1995) Cornish Mineral Reference Manual. Endsleigh Publications |
| Reid, C., Flett, J.S., Wilkinson, B.S.N., Dixon, E.E.L., Pollard, W., and MacAlister, D.A. (1907): The Geology of the Land's End District. HMSO Publications (London), p. 114. |