Vaterite from Ballycraigy, Larne, Northern Ireland

J. D. C. McConnell
Dept. of Mineralogy and Petrology, Downing Place, Cambridge

Summary: Vaterite, the third unstable polymorph of CaCO3, is recognized by optical and X-ray powder techniques as a major constituent in a carbonated calcium silicate hydrogel complex formed from larnite at Ballycraigy, Lame, Northern Ireland. Re-indexed X-ray powder data obtained on synthetic vaterite are provided indicating a hexagonal unit cell with dimensions a = 7·135 Å. and c = 8·524 Å., Z = 6CaCO3. The re-indexing is endorsed by the results of electron diffraction study of synthetic vaterite. Vaterite is shown to correspond to the hypothetical CaCO3 member of the bastnäsite-synchisite mineral series on the basis of extrapolated cell dimensions and optical properties. A structural scheme for vaterite is proposed in which Ca layers replace the CeF layers in bastnäsite, and near-vertical CO3 groups are present. The stability relations of natural vaterite are discussed and comment made on the recent observation of vaterite, in a like environment, in carbonated cements and mortars.

Mineralogical Magazine; September 1960 v. 32; no. 250; p. 535-544; DOI: 10.1180/minmag.1960.032.250.03
© 1960, The Mineralogical Society
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