Optical Calcite from José María Patoni, Mexico – Clear Cleavage Rhombohedron

This optical Calcite from José María Patoni near San Juan del Río in the Mexican state of Durango is a transparent to locally slightly milky cleavage piece showing the characteristic strong double refraction of Calcite. Lines and writing viewed through the specimen appear clearly doubled or displaced.

Measuring 3.1 × 2.5 × 1.6 cm and weighing 34.5 g, this is a miniature specimen. The piece occurs as a typical cleavage rhombohedron, clearly demonstrating both the perfect rhombohedral cleavage and the pronounced optical properties of Calcite.

Transparent optical Calcite with distinct double refraction

The Calcite is predominantly colorless and transparent. Marginal areas and individual zones appear slightly milky or are somewhat clouded by internal cleavage structures.

Its most characteristic feature is the double refraction. When writing or lines are viewed through the Calcite, they appear clearly doubled due to the strong birefringence of the mineral. This optical effect is clearly visible in the product photographs.

Natural cleavage planes, fine internal fractures and structural features are visible within the specimen. These are part of the natural internal structure of the Calcite.

Cleavage rhombohedron of optical Calcite

Calcite has perfect rhombohedral cleavage. When the mineral is split along these natural cleavage directions, characteristic rhombohedral pieces are produced, commonly referred to as cleavage rhombohedra.

The shape therefore should not be confused with the natural crystal habit of a freely grown Calcite crystal. It results from cleavage along the mineral’s natural planes and is particularly well suited to demonstrating its optical properties.

Optical Calcite from José María Patoni, Durango

The deposits of José María Patoni (Menores de Arriba), San Juan del Río, Durango are well known for high-quality optical Calcite. Transparent Calcite from this locality has long been valued for its clarity and pronounced double refraction.

This specimen combines a classic locality for optical Calcite with a clearly visible optical effect, making it both an interesting collector specimen and an excellent demonstration piece for the double refraction of Calcite.