Dolomite

This specimen is dolomite, a calcium–magnesium carbonate mineral closely related to calcite but distinguished by its magnesium content and typically greater hardness. The rock displays a fine-grained, massive texture with muted pink-to-brown tones, characteristic of dolomite-rich sedimentary units in northwest New Zealand. One face of the specimen has been cut and polished, revealing the dense crystalline fabric and subtle internal colour variations that are less visible on natural surfaces. The remaining faces retain their natural weathered texture, providing a useful contrast between raw and prepared material. Dolomite commonly forms through the chemical alteration of limestone, where magnesium-rich fluids replace part of the calcium in calcite. In the Collingwood region, dolomite is associated with Paleozoic sedimentary sequences that have experienced low-grade metamorphism and hydrothermal alteration.