G. J. Brush on Ralstonite. 31 
planes alike in lustre I cannot doubt that they are isometric 
octahedrons, and hence that the small plane on the angles is a 
cubic plane. 
The mineral is colorless to white, with a vitreous luster, and 
has a hardness greater than fluorite, equal to about 4°. 
Specific gravity, taken on 25 milligrams, gave 2°4. 
