Mineral Species: Mimetite var. Campyllite 

Chemical Formula: Pb5(AsO4)3Cl

Chemical Name: Lead Chloroarsenate

Mineral Class: Arsenate

Mineral Notes: Mimetite forms in secondary, weathered zones of lead ore deposits. It is very similar in composition to Pyromorphite, the difference being the substitution of the Arsenate ion by Phosphate. Campyllite is a variety of Mimetite characterised by barrel-shaped orange-yellow crystals. 

Description: This is specimen of considerable rarity on account of the extremely well-formed Campyllite crystals. These show the barrel-shaped habit extremely well. The colour is an attractive yellow brown and the crystals have a strong glassy luster. The specimen comes from the collection of Bill Crighton.

Location: Dry Gill Mine, Caldbeck Fells, Cumbria, England.