In 1941 the Home Ore Department of Iron and Steel Control, Ministry of Supply, took over the old Benallt manganese mine at Rhiw in the Lleyn Peninsula, Carnarvonshire. A new shaft was sunk and a new mine was developed among and mainly below the old workings. It was in one of the old workings of Benallt that Mr. (now Sir) Arthur Russell discovered in 1911 the well-crystallized specimens of celsian and paracelsian recently described by Dr. L. J. Spencer.

Dr. A. W. Groves of the Mineral Resources Department of the Imperial Institute and geologist to the Home Ore Department had had a sharp look-out kept for the reappearance of the barium-felspars in the new workings, and when thin bands of coarsely crystallized but compact, white ‘sparry’ minerals were found in one of the ore-bodies he sent specimens to the Department of Mineralogy of the British Museum for investigation.

It seems to be a peculiarity in the history of the diamond that from time to time operations which have been known from time immemorial are re-invented and claimed to be new. For instance, cleaving, which is said to have been known to the Indians, was discovered again by W. H. Wollaston. It is obvious, too, that cleaving was already known to A. B. de Boodt in 1604. The same applies to the sawing of gems by a thin rotating disk, which seems to be as old as the engraver's treadle lathe (earliest reference about 1520) ; but this art does not seem to have been applied to diamonds, as the first reference to diamond sawing with a thin rotating blade is that in 1874. All previous references seem to be to the sawing of diamonds with a thin wire moistened with a paste of diamond dust and oil, and otherwise designated as the Chinese method. Other gemstones, were always sawn with thin disks on lapidaries' benches with vertical spindle. Similar remarks may be applied to bruting and drilling, but only polishing seems to have always been recognized as the main operation.