Pyromorphite-Mimetite

specimen number:
2102256

location:
South Vein, Driggeth Mine, Caldbeck Fells, Cumbria, England, UK

description:

Classic specimen from this locality, lustrous green somewhat rounded crystals to 0.3 cm in size thickly covering a quartz rich matrix. In good condition.

The Driggeth Mine is located in the Caldbeck Fells of Cumbria, England, situated on the northern slopes of High Pike. Geologically, the mine worked a series of east-west trending hydrothermal veins that cut through the Ordovician-aged Eycott Volcanic Group, primarily consisting of basaltic andesites. These veins are part of a complex multi-stage mineralization event involving lead, copper, and zinc, which later underwent significant secondary oxidation to create a diverse suite of rare minerals. Historically, mining at Driggeth dates back to the Elizabethan era in the late 1500s, though the most intensive period of industrial activity occurred between the 1840s and 1870s under various operators like the Driggeth Mining Company. While the mine produced substantial quantities of galena and copper ores, it eventually closed in the early 20th century, with final attempts at barytes and lead recovery ending around 1950. Today, the site is a protected area of scientific interest, famous among mineralogists for producing world-class specimens from the oxidation zone of the veins.

The pyromorphite-mimetite series represents a complete solid solution between lead phosphate and lead arsenate, both belonging to the apatite group. In this series, phosphorus and arsenic can freely substitute for one another in the crystal lattice, leading to a continuum of minerals where the distinction is based on which element is more dominant. Pyromorphite is the phosphorus-rich end-member, typically appearing in shades of bright green or yellow-green, while mimetite is the arsenic-rich end-member, often exhibiting yellow, orange, or reddish-brown hues. These minerals are secondary in origin, forming in the oxidized zones of lead-bearing ore deposits where they often create spectacular hexagonal prisms or barrel-shaped crystals known as campylite. Because the Caldbeck Fells region is rich in both phosphorus and arsenic, the Driggeth Mine has produced a wide variety of specimens that span this chemical series, often showing beautiful intermediate colors and complex crystal habits.

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