Mica.

The Scientific American 2, 9.1.1869

An esteemed correspondent gives the following: "Base-burning coal stoves are now all the rage, and the illuminating part of them is what takes. So many of this kind of stoves are now being made that the question of clear white mica for this purpose is becoming important. There are hundreds of different inferior grades of mica. "Canada Mica" is of several different shades, from the light brown to the intensely black. New York gives us good mica, but no mica can be had equal to that found in the Eastern States. The demand has been so great for the past two or three years that the supply from the Eastern States has been exhausted, at least the mines at present open; what further development can be made remains to be seen. Mica has been so scarce during the past season that it has commanded the most unheard of prices. Six dollars being a common rate per pound and some qualities selling as high as twelve dollars per pounds."