Actinolite

This specimen is composed predominantly of actinolite, a calcium–magnesium–iron amphibole mineral that commonly forms during low- to medium-grade metamorphism of mafic or ultramafic rocks. The elongated, bladed to fibrous crystal habit visible on the surface is characteristic of actinolite and reflects its amphibole crystal structure.

Actinolite is frequently associated with greenschist-facies metamorphic environments, and its green coloration arises from iron content within the crystal lattice. Specimens from the Taipo River region of Westland are typically derived from metamorphosed volcanic or ultramafic parent rocks within New Zealand’s complex accretionary and orogenic terranes.

This example appears as a massive, flattened fragment, likely water-worn prior to collection, suggesting transport within a river system before deposition. Actinolite plays an important role in understanding metamorphic conditions and fluid activity in tectonically active regions such as the South Island.

147 x 56 x 20mm

236g