According to the book, Gemstones of the World, Sterling Publishing,
basanite is a “black, fine-grained jasper from North Carolina used by
jewelers and goldsmiths for streak tests of precious metals”.
According to the Dictionary of Gems and Gemology by Robert M. Shipley,
published by the GIA, it is a " Lydian stone, or touchstone. Velvety
black quartz used for testing the color of the streak of metals".