Pound, coarsely, some of the dark blue or the fetid variety of
Derbyshire spar; heat it in a dark room, in a platinum spoon, over the
low flame of a spirit-lamp, and the spar will shine with a beautiful
purple tint.
Pounded swinestone, calcareous spar, and powdered quartz, will also
give out light, if strewn upon a fire-shovel which has been heated
red-hot, and has just ceased glowing.
A variety of fluor spar, found in granite in Siberia, will shine in
the dark when warmed, with a remarkably strong phosphorescent light,
increasing as the temperature is raised. The light augments when the
spar is plunged into water; and in boiling water, the spar becomes so
luminous that the letters of a printed book can be seen in a dark room
near the glass containing it.
Another variety of fluor spar, also found in Siberia, is of a pale
violet colour, and emits a white light merely by the heat of the hand;
and when put into boiling water, it will give out a green light.