Dogtooth spar is a

speleothem A speleothem (; ) is a geological formation by mineral deposits that accumulate over time in natural caves. Speleothems most commonly form in calcareous caves due to carbonate dissolution reactions. They can take a variety of forms, depending ...

that consists of very large calcite crystals resembling dogs' teeth. They form through mineral precipitation of water-borne calcite. Dogtooth spar crystals are found in caves, open spaces including veins and fractures, and

geode A geode (; ) is a geological secondary formation within sedimentary and volcanic rocks. Geodes are hollow, vaguely spherical rocks, in which masses of mineral matter (which may include crystals) are secluded. The crystals are formed by the fill ...

s. 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 triangle A triangle is a polygon with three edges and three vertices. It is one of the basic shapes in geometry. A triangle with vertices ''A'', ''B'', and ''C'' is denoted \triangle ABC. In Euclidean geometry, any three points, when non-collinear ...

s. However, modification of these faces is common, and some may have many more than three edges. Calcite crystallizes in the rhombohedral system, and the most common scalenohedron form has the

Miller index Miller indices form a notation system in crystallography for lattice planes in crystal (Bravais) lattices. In particular, a family of lattice planes of a given (direct) Bravais lattice is determined by three integers ''h'', ''k'', and ''� ...

Spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

is a general term for transparent to translucent, generally light-colored and vitreous crystalline minerals.

References

External links

The Virtual Cave:Spar
Speleothems {{Mineral-stub