Quick Note

Not all white deposits are calcium sulphate

This note was posted to the Titanium Bolting FB Group 16 January 2020

A consistent feature of the “sulphur crag” story, especially at Railay/Tonsai is that sulphate is not found any distance more than 100m or so from the sea.

Thus it is no surprise that the white deposit found at Wee’s Present Wall shown below, is not sulphate. It is very difficult to wet, let alone show any solubility in 1M HCl. I’m not sure what it can be, but suspect it might be partially organic in nature.

Taking swabs of the rock surface revealed no trace of sulphate.

The same phenomenon can be seen along the track from Railay East to Pra Nang. White deposits are commonplace, but there is no trace of sulphate until you are within 50m of the sea, and then vey high levels are suddenly encountered.

There are multiple lines of evidence that point to the sulphur source being the marine coarse aerosol fraction of >20um diameter. It is rapidly attenuated by gravitational drop-out and impact with vegetation.

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