Pyromorphite, Pb5(PO4)3Cl (Lead Chlorophosphate), is analogous to Mimetite with the Phosphate (PO4) 3- ion replacing the Arsenate cation. Although the properties of the two minerals are almost the same because of this, colour can usually be used to distinguish between the two, Mimetite being yellow and Pyromorphite being yellow-green. It is a secondary mineral ocassionally used as an ore of lead. 

Description: A dark brown limestone matrix upon which sits a black, porous deposit of iron oxide. Interspersed in the cavities and raised areas are rich aggregates of yellow-green Pyromorphite. Whilst many of the aggregates are amorphous masses, many areas contain groups of fibrous crystals. This unusual habit is rare and the crystals have a distinct waxy luster. Around the sides of the matrix are numerous areas of green Pyromorphite many of which have fused into platy scales.

Location: Iron Crag, Caldbeck Fells, Cumbria, England.