Fraipontite

Crystal System: Orthorhombic,Monoclinic
Status of Occurrence: Confirmed Occurrence - 3rd UK recording
Distribution: Rare
Chemical Composition: Zinc aluminium silicate hydroxide
Chemical Formula: (Zn,Al)3(Si,Al)2O5(OH)4
Method(s) of Verification: Machen Quarry - XRD at the National Museum of Wales (X-ray film numbers, NMW X-850 & 851) & Oxford University Museum. All patterns are feint with diffuse lines.

Chemical Group:

  • Silicates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
Introduction: fraipontite is a secondary zinc-bearing clay mineral found in oxidized zinc-bearing mineral deposits.
Occurrence in Wales: a rare mineral in the British Isles fraipontite was, discovered in the late summer of 1993, in samples collected from lead-zinc bearing brecciated calcite-baryte veins cutting Carboniferous Limestone on Bench no. 9 of Machen Quarry (Goulding & Price, 1995). Crystallized specimens are extremely rare, however, fractured botryoids resembling hyrozincite were found, following X-ray analysis at the National Museum of Wales, to be fraipontite (Plant & Jones, 1995). Therefore, fraipontite may in fact be more common at Machen than first thought, but requires detailed analysis to be certain.

Key Localities:

  • Machen Quarry, Caerphilly, South Wales: individual pearly, pale green, hexagonal or pseudohexagonal crystals up to 0.4 mm across and foliated masses on hemimorphite within a couple of cavities in brecciated calcite-baryte-galena veinstone (Goulding & Price, 1995). Also as small waxy creamy-white fractured botryoids resembling hydrozincite (Plant & Jones, 1995). Only a small number of specimens have ever been collected.

There are no key localities for this specimen.

References:

  1. Goulding, J., and Price, M.T., 1995. Well-crystallised fraipontite from Machen quarry, Mid Glamorgan: A first Welsh locality. Journal of the Russell Society, 6(1), 50.
  2. Plant, S.P. & Jones, I.E., 1995. Minerals of Machen Quarry, Mid Glamorgan, Wales. Journal of the Russell Society, 6(1), 31-36.

There are no references for this specimen.