Crandallite

Crystal System: Hexagonal
Status of Occurrence: Confirmed Occurrence
Distribution: Uncommon
Chemical Composition: Calcium aluminium phosphate hydroxide hydrate
Chemical Formula: CaAl3(PO4)2(OH)5.H2O
Method(s) of Verification: Pwlldu - XRD & EPMA (National Museum of Wales, NMW X-1334).

Chemical Group:

  • Phosphates

Geological Context:

  • Supergene: in situ natural oxidation & weathering deposits
White, powdery crandallite coating chert from Pwlldu beach, Gower, South Wales. Field of view 7 mm wide. National Museum of Wales Collection (NMW 2002.23G.M.1). Photo D.I. Green, © National Museum of Wales.
Introduction: crandallite is a secondary mineral that typically occurs in weathered, aluminium-bearing, phosphatic rocks and nodules. It also occurs in unusually phosphate-rich pegmatites and hydrothermal mineral veins and may have a wide range of mineral associates.
Occurrence in Wales: Dean & Cotterell (2003) produced the first record of crandallite from Wales, describing white chalky masses replacing altered wavellite within chert washed up on a storm beach on the Gower Peninsula. Although only a few specimens have been recorded to date, it is worth recording that due to its indistinct appearance crandallite may be easily overlooked.

Key Localities:

  • Pwll-du storm beach, Bishopston, Gower, South Wales: crandallite occurs as creamy-white powdery coatings on chert and rottenstone and as chalky white masses often showing the relict structure of the wavellite from which it has formed (Dean & Cotterell, 2003).

References:

  1. Dean, A. & Cotterell, T.F., 2003. Cacoxenite and crandallite from Pwlldu Beach, Bishopston, Gower, Swansea, South Wales: The first Welsh occurrence. Journal of the Russell Society, 8(1), 30-32.