Mimetite, Pb5(AsO4)3Cl (Lead Chloroarsenate), 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 small orange-yellow rounded crystals.

Description: An excellent example of this mineral from a classic location. A grey-black matrix hosting a mass of semi-transparent quartz pyramids. Upon a number of these towards the front of the specimen is a single large botryoidal mass of Campyllite. The spheroid is highly crystalline, the classic yellow-brown colour and has a bright waxy luster. A first class specimen from an extremely rare location.

Location: Iron Crag Mine, Caldbeck Fells, England.