Dolomite / Quartz,Tan y Foel quarry.

Dolomite / Quartz,Tan y Foel quarry.

Dolomite, CaMg(CO3)2. Tan y Foel quarry, Cefn Coch, Nr Welshpool, central Wales. The quarry provides a section through the Wenlock, mid Silurian, sedimentary deposits. The rocks belong to the Penstrowed Grits Fm. The specimen is an example of material from the occasional fault within the quarry, and shows veins filled with dolomite and quartz. A small vugh has allowed the growth of clear quartz crystals and numerous tiny dolomite crystals which display the familiar curved faces.A very similar specimen was obtained from Penstrowed quarry, Newtown.

Galena on Quartz, Dylife. (CWO)

Galena on Quartz, Dylife. (CWO)

Galena, PbS, and Quartz, SiO2. Dylife mine, Nr. Staylittle, Central Wales Orefield. Pieces of brecciated material with a very fine coating of druzy quartz, on which are scattered flattened crystals of galena.The base rock is very light grey in colour.

Sphalerite / Quartz, Bryn y Rafr. (CWO)

Sphalerite / Quartz, Bryn y Rafr. (CWO)

Sphalerite, ZnS, and Quartz, SiO2. Bryn y Rafr mine, west Wales. Several layers of sphalerite separated by quartz. There are no observable crystals in the sphalerite or the quartz. The quartz has reddish colour, which is probably from iron staining.

Calcite, Dylife. (CWO)

Calcite, Dylife. (CWO)

Calcite, Calcium carbonate, CaCO3. Dylife mine, Nr. Staylittle, Central Wales Orefield. Two larger flattened rhombohedral crystals,and a scattering of smaller crystals on a bed of fine druzy quartz.

Pyromorphite,Bwlch Glas.

Pyromorphite,Bwlch Glas.

Pyromorphite, Pb5(PO4)3Cl. Bwlch Glas mine, Nr. Talybont, west Wales. Some stubby, some elongated, barrel shaped crystals. Colouration mostly light to dark green, but with a few almost colourless crystals.