Terra ponderosa From Strontian

In 1787, a mineral was found in a lead mine in Strontian, Scotland, that proved difficult to identify. It was considered to be a kind of witherite, barium carbonate. Dr Adair Crawford (1748-1795) took an interest in the substance because at his hospital. Saint Thomas in London, he prepared barium chloride from carbonate and examined the medical properties of the chloride. 

He was an Irishman educated in Glasgow, and he later became professor of chemistry in Woolwich. At his hospital in London Dr Crawford heard about the new bari- 

Phosphorescence is one type of luminescence (Latin, lumen-light). When certain materials absorb energy (from sunshine or from a UV-lamp), the electrons become excited and jump from the inner orbits of the atoms to the outer. When the electrons fall back to their original state, a photon of light is emitted. The interval between the two steps may be short or long. If the interval is short, the process is called/lwo- 

In the actual case of Bolognian Stone, perhaps BaS is formed together with a certain excess of Ba, dissolved interstitially. The stone then behaves like an impure semiconductor, displaying phosphorescence. 

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