Barite after Alstonite with Sphalerite

specimen number:
2102136

location:
2nd Sun Vein, Haggs Mine, Alston Moor, England, UK

description:
Sharp crystals of what were once alstonite measuring to 0.3 cm in size, these now replaced by white crystalline barite, and scattered across a crystallized quartz matrix with lustrous black crystals of sphalerite. Collected in the very early 1990s. In very good condition. Interesting specimen for this British locality. Galena and dolomite are present as well.

Alston Moor, located in Cumbria, England, is one of the most historically important mining areas in the Northern Pennine Orefield, with a long history of lead mining dating back to at least the 17th century. The region is characterized by extensive vein systems cutting through limestone, sandstone, and shale, which hosted deposits of galena along with associated minerals such as sphalerite, fluorite, baryte, and calcite. Mining was carried out through numerous small mines and levels spread across the moor, with production peaking in the 18th and 19th centuries. The area became well known not only for its lead output but also for the fine mineral specimens it produced, many of which are now found in museum and private collections. Decline in lead demand and changing economic conditions led to the gradual closure of most operations by the early 20th century.

Pseudomorphs are minerals that have replaced an earlier mineral while preserving the original external crystal form, creating a specimen that has the shape of one mineral but the composition of another. In the case of barite after alstonite from Alston Moor, the original alstonite crystals were chemically altered and replaced by barite, often retaining the distinctive crystal habit of alstonite. These pseudomorphs can be especially interesting to collectors because they record a sequence of mineral formation and alteration within the deposit. At Alston Moor, such specimens are valued for both their aesthetic appeal and their geological significance, as they provide insight into the changing chemical conditions within the mineralizing system over time.

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