Those stones which show electricity on the application of pressure are such as the fluorspar, calcite, and topaz.
"The Chemistry, Properties and Tests of Precious Stones"
John Mastin
In order to be used in steel-making, the fluorspar after being concentrated should contain at least 85 per cent calcium fluoride and less than 4 per cent silica.
"The Economic Aspect of Geology"
C. K. Leith
The chief foreign producer of fluorspar is Great Britain, and much of this product comes to the United States.
"The Economic Aspect of Geology"
C. K. Leith