Serpentine?

This specimen is a dark green to olive-green rock with a slightly greasy to dull surface lustre, characteristic of serpentine-rich rocks. The material appears massive rather than crystalline, with subtle colour zoning and areas of weathering producing rusty orange staining along exposed surfaces. Serpentine forms through the alteration of ultramafic rocks (such as peridotite) during low-temperature metamorphism, where water reacts with magnesium-rich minerals deep in the Earth’s crust. The Red Hills area of New Zealand is well known for extensive ultramafic and serpentinised rocks, making serpentine a geologically plausible identification for this specimen.