BENSTONITE
Benstonite is a rare, barium-calcium-magnesium
carbonate mineral, Ba6Ca6Mg(CO3)13.
Chemical studies show that strontium and manganese often substitute for the
barium and calcium respectively. Benstonite has a nonmetallic, glassy
luster, a white to off-white to pale yellow to yellowish-brown color, a white
streak, a hardness of 3 to 4, and has good cleavage. It forms
translucent, rhombohedral crystals. The best benstonite specimens on
Earth are from Illinois' Cave-in-Rock Mining District.
Benstonite from the Bethel Level, Minerva # 1 Mine, Cave-in-Rock Mining District,
southern Illinois, USA.