Caryopilite

Crystal System: Monoclinic
Status of Occurrence: Confirmed Occurrence - 1st UK recording
Distribution: Rare
Chemical Composition: manganese magnesium silicate hydroxide
Chemical Formula: (Mn,Mg)3Si2O3(OH)4
Method(s) of Verification: Nant Mine - XRD & EMPA (National Museum of Wales, X-ray reference numbers: NMW X-1522, 1536, 1601 & 1606).

Chemical Group:

  • Silicates

Geological Context:

  • Metamorphic: low-grade
Caryopilite veinlet cutting manganese ore from Nant-y-Gadwen, Ll?n. Field of view 8 mm across. National Museum of Wales Collection (no. NMW 37.676.GR.28c). Photo T.F. Cotterell, © National Museum of Wales.
Introduction: a rare kaolinite-serpentine group mineral typically formed through the alteration of primary manganese silicates, including rhodonite, in metamorphosed manganese deposits.
Occurrence in Wales: Cotterell (2006) discovered caryopilite forming thin veinlets within a specimen of siliceous manganese ore in the collections of the National Museum of Wales. The specimen, labelled as from Nant-y-Gadwen, Rhiw, Llŷn, Gwynedd was acquired by the National Museum of Wales from Dr. A.W. Woodland in 1937. Dr. Woodland published a number of papers on the petrography of manganese ores of North Wales.

Key Localities:

  • Nant Mine, Nant-y-Gadwen, Rhiw, Llŷn, Gwynedd: thin (< 0.25 mm) orange-brown, felt-like veinlets cutting massive, dense, siliceous manganese ore from Nant-y-Gadwen was identified as caryopilite by Cotterell (2006). Subsequently, specimens of caryopilite veined calcite were collected from the dumps of Nant Mine situated near to the top of the incline down to the beach where the ore was shipped.

References:

  1. Cotterell, T.F., 2006. Caryopilite and pyroxmangite from Nant Mine, Nant-y-Gadwen, Llanfaelrhys, Pen Llyn, Gwynedd, Wales UK Journal of Mines and Minerals, 27, 51-53.