Calcite from Nieder-Werbe near Kassel – Intergrown Crystals on Greywacke

This Calcite specimen from the greywacke quarry at Nieder-Werbe near Kassel, Germany, shows numerous small, densely intergrown Calcite crystals on a gray-brown matrix. The crystals cover several areas of the specimen and form an irregular, finely crystallized surface.

Measuring 10.3 × 5.5 × 5.0 cm and weighing 274.2 g, this is a large cabinet specimen. The Calcite crystals are predominantly small and do not occur as isolated free-standing crystals, but instead form densely intergrown groups on the matrix.

Densely intergrown Calcite crystals

The Calcite crystals are colorless to pale gray and beige and are partly translucent. Because of the dense intergrowth of the numerous small crystals, larger areas are only weakly light-transmitting. Gray areas of the mineralization appear opaque.

The surface shows numerous small crystal faces with a dull to locally weak luster. Several cavities and depressions within the matrix contain additional Calcite crystallization and give the specimen a three-dimensional structure.

Calcite from the Nieder-Werbe greywacke quarry

The greywacke quarry at Nieder-Werbe is known for various fracture minerals. Mineral-bearing fluids circulated through tectonically formed fractures and cavities, from which Calcite, among other minerals, crystallized.

This specimen shows a typical fracture mineralization with densely intergrown Calcite on greywacke. Its appeal lies less in large individual crystals than in the extensive crystallization, the several cavities, and the clear contrast between the pale Calcite and the darker areas of the matrix.