Specimens of this ore, when kept for some time undisturbed, on being opened out were covered with a white incrustation, having the appear- ance of minute crystals.

Can any of your readers account for this circumstance ? Richmond, Yorkshire, August 4 1832.

It is impossible to say, from the above description, what ore of iron is alluded to ; nor is the phrase " opening out" properly explained.

Most likely ( the specimen" is a mass of radiated or of hepatic pyrites (sulphuret of iron), very common, in the radiated form, in some beds of the chalk formation, as at Cherryhinton, near Cambridge, Godstone, Surrey.

When exposed to the air, the oxygen unites with the sulphur ; and a white silky efflorescence, or " minute crystals," result from the decomposition.