Dogtooth spar

Dogtooth spar crystals are found in caves, open spaces including veins and fractures, and geodes.

[1] The crystals are generally centimeters long, but anomalous samples decimeters long exist, notably in Sitting Bull Crystal Caverns.

A layer of crystalline calcite can be found underneath the surface of crystal points.

The crystals typically consist of acute scalenohedrons, twelve triangular crystal faces that ideally form scalene triangles.

Calcite crystallizes in the rhombohedral system, and the most common scalenohedron form has the Miller index [2131].

Dogtooth spar deposited on the walls of a part of the Caverns of Sonora near Sonora, Texas . The former water level can be seen in the upper left hand corner.