(Strontian variety of benstonite.

Comparison is made of the Sr-rich (SrO 10-11%) variety of benstonite from the Murun alkali massif, Siberia, with benstonites previously described from Arkansas, India and elsewhere. The Murun benstonite, Sr1.71(Ba3.68Ca0.25)3.93Ca7C13.2O39, has a 18.23, c 8.67 A; epsilon 1.660, omega 1.680; D 3.38 g/cm3. The DTA curve shows endothermic effects at 600o, 840-850o and 900oC. The Murun and Arkansas benstonites are part of an isomorphous series Ba6Ca7(CO3)13-Sr6Ca7(CO3)13. -R.A.H.