Stilbite

This specimen features stilbite, a calcium–sodium aluminium silicate belonging to the zeolite mineral group. Stilbite commonly forms radiating, fan-shaped or sheaf-like crystal aggregates, which are clearly visible here as peach to pale salmon-coloured bladed crystals. Stilbite forms in low-temperature hydrothermal environments, most often within cavities (vesicles) in volcanic rocks such as basalt. Mineral-rich fluids circulate through the rock after eruption, slowly depositing zeolite minerals as the fluids cool. The Awatere Valley is well known for producing zeolite minerals, particularly stilbite and natrolite, from altered volcanic sequences. Crystals of stilbite are prized for their distinctive crystal habit and soft, pearly lustre. While relatively soft, stilbite plays an important role in geological studies as an indicator of secondary mineral formation and fluid movement within volcanic terrains.