68.—Spinel Ruby.
Occurs in pyramidal crystals; glassy lustre; powder white; scratches rock-crystal; by heat becomes black; gravity 3.5.
Value.—A gem; clear specimens weighing over four carats, are valued at half the price of the diamond.
Localities.—Found in granular limestone and clay. Amity and Gouverneur, N. Y.; Franklin and Byram, N. J.; Bolton and Boxborough, Mass.