Analysis of the white 'efflorescence' showed the material to consist predominantly of calcium sulphate (approximately 95%) with a small quantity of calcium carbonate.
Precipitated white crystals in substantial quantities have not been noted previously by the EAU in 'waterlogged' deposits in York, and no analyses have been carried out in the past. It is suggested that the formation of the calcium sulphate at Parliament Street is related to the postulated oxidative degeneration of the deposits. A likely mechanism is downward movement of calcium ions from the overlying concrete raft in oxygen-bearing water, perhaps encountering sulphide ions in the highly organic and originally anoxic layers beneath.
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Last updated: Wed Mar 6 2002