Hyperstein, Labrador Hornblende

This substance, now called Hyperstein, was formerly considered as an Hornblende. It was sent me some years ago as a common mineral from the vicinity of Aberdeen. It differs from Hornblende in the form of its nucleus, which is a rhomboidal prism of about 100°. Some varieties of Schiller Spar or Diallage (Brit. Min. tab. 334.) very nearly resemble it; but they are laminated only in one direction, and their cross fracture has a waxy appearance, whereas the cross fracture of Hyperstein is ragged and somewhat splintery. The metallic lustre appears to arise, in a great measure, from a commencement of decomposition, as those parts which are nearest to the exposed surface of the specimen possess it in the most eminent degree. It is imbedded in Feldspar of a gray colour: and although more liable to decomposition, its superior hardness defends it longer against the effects of weather and water. The Spec. Grav. according to Haüy is 3.4.

The specimens from Labrador are generally blacker but in other respects scarcely different.