Calciostrontianite in the basal Purbeck beds of

Summary. A spherulitic mineral occurring as veins and nodules in celestine-bearing secondary limestones in the Lower Purbeck Beds at DurLston Head, Swanage, Dorset, is identified as calciostrontianite, a mineralnot previously recorded from Britain. Textural relationships indicate that it was formed from the alteration of celestine and was in part converted back into celestine. The calciostrontianite originated as an epigenetic mineral during the tectonic movement that gave rise to the Broken Beds. V EINS of a spherulitic mineral composed of acicular radiating crystals, soluble in dilute hydrochloric acid and reacting positively to alizarin stains for calcite, were recorded in the basal Purbeck Beds at Durlston Head near Swanage (SZ 035772) and referred to as calcite (West, 1960). X-ray dif[ractometry by D. L. Salter has since shown them to be of calciostrontianite, a mineral once called emmonite (Thomson, 1836). The Purbeck calciostrontianite h re described con-sists of spherulites or partial spherulites usually ranging from 0"1 to 1"0 mm in diameter (fig. 1) that closely resemble those described b