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: A good example of this mineral from a classic location. A grey-black matrix hosting a single large botryoidal mass of Campyllite. The spheroid is highly crystalline, the classic yellow-brown colour and has a bright waxy luster. On the surface of the matrix are other numerous thin crusts of crystalline Campyllite, although none forms another whole sphere. A great location specimen.

Location: Dry Gill Mine, Caldbeck Fells, England.