Intrigued by Mark Thomas' youtube video of the Brunton calciner at Wheal Busy,



and his claim that the thick colloform coating of much of the underside of the building was arsenolite (As2O3), I managed to convince my wife that we should pay a visit after a walk around Killifreth and the woods. Due to the high solubility of As2O3 in water, my prejudice was it was nothing more than gypsum leached from the cement (as seen in deposits coating masonry at Wheal Betsy, Mary Tavy), so I sampled a small amount from under the hearth where the deposit is thickest.

Egg on face moment when qualitative X-ray Fluorescence showed not only a strong signal from calcium and sulphur (gypsum) but also a significant signal from arsenic. X-ray diffraction indicated major gypsum and pharmacolite (CaHAsO4 2H2O) - the arsenic analogue of brushite (was glad my blind physics prejudice didn't overrule chemical common sense when taking samples).

Pharmacolite is known to grow pseudoepitaxially on gypsum (crystal structures and space groups closely related), so the coexistence makes chemical/crystallographic sense.

Rodriguez-Blanco et al, Crystal Growth and Design 7 (2012) 2756-63.

Full phase identification by further XRD is still being undertaken; arsenolite and claudetite (polymorphs of As2O3) are not present in the sample, but weilite and haindigerite (other Ca arsenates) have been reported from other calciners in the West Country.

As the presence of pharmacolite means low levels of arsenic in solution, I guess that the bottom line is that exploring these old arsenic works should not be taken on lightly, and furthermore, as these are not considered to be minerals sensu-stricto, hopefully the mineral collecting fraternity will also give them a wide berth.

We are back down this way in early Summer, so I shall sample more systematically this time to see if there is a variation with location in the calciner.

Kevin

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Intrigued by Mark Thomas' youtube video of the Brunton calciner at Wheal Busy,

Interesting video but 28 minutes is too much for me I only have an attention span of 5 minutes 🙂

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Intrigued by Mark Thomas' youtube video of the Brunton calciner at Wheal Busy,

and his claim that the thick colloform coating of much of the underside of the building was arsenolite (As2O3), I managed to convince my wife that we should pay a visit after a walk around Killifreth and the woods. Due to the high solubility of As2O3 in water, my prejudice was it was nothing more than gypsum leached from the cement (as seen in deposits coating masonry at Wheal Betsy, Mary Tavy), so I sampled a small amount from under the hearth where the deposit is thickest.

Egg on face moment when qualitative X-ray Fluorescence showed not only a strong signal from calcium and sulphur (gypsum) but also a significant signal from arsenic. X-ray diffraction indicated major gypsum and pharmacolite (CaHAsO4 2H2O) - the arsenic analogue of brushite (was glad my blind physics prejudice didn't overrule chemical common sense when taking samples).

Pharmacolite is known to grow pseudoepitaxially on gypsum (crystal structures and space groups closely related), so the coexistence makes chemical/crystallographic sense.

Rodriguez-Blanco et al, Crystal Growth and Design 7 (2012) 2756-63.

Full phase identification by further XRD is still being undertaken; arsenolite and claudetite (polymorphs of As2O3) are not present in the sample, but weilite and haindigerite (other Ca arsenates) have been reported from other calciners in the West Country.

As the presence of pharmacolite means low levels of arsenic in solution, I guess that the bottom line is that exploring these old arsenic works should not be taken on lightly, and furthermore, as these are not considered to be minerals sensu-stricto, hopefully the mineral collecting fraternity will also give them a wide berth.

We are back down this way in early Summer, so I shall sample more systematically this time to see if there is a variation with location in the calciner.

Kevin

Well done. You;ve probably just condemned another piece of Cornish history to the bulldozer!

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There is a lot of hysteria regarding arsenic. If it is an issue where are the piles of bodies? People have been safely exploring arsenic contaminated sites for decades, it really isn't a problem.

At last someone with a bit of common sense. You don't go into arsenic workings like labyrinths etc without exercising acertain precautions. The arsenic labyrinth at south polgooth is well preserved and is worth a visit. Not just for the arsenolite but for the architectual features still preserved there.
:)

Um, it's an arsenic calciner, there will be some arsenic present, don't lick it, simples

Um, it's an arsenic calciner, there will be some arsenic present, don't lick it, simples

Exactly what i was thinking... :lol::thumbsup::lol: