Nepheline-bearing Diorite (Porphyritic)

This specimen is an alkaline igneous rock containing conspicuous pinkish feldspar phenocrysts set within a darker, fine- to medium-grained groundmass. The presence of nepheline, a silica-undersaturated feldspathoid mineral, distinguishes this rock from typical granite or diorite and places it within the alkaline intrusive rock series.

Although the handwritten label reads “Nepheline,” this reflects a common older collecting practice of naming a specimen after its most notable or diagnostic mineral rather than the full rock type. In modern geological usage, the specimen is best described as a nepheline-bearing diorite or nepheline syenitic variant, depending on precise mineral proportions.

Rocks of this type are relatively uncommon and are associated with alkaline magmatism, where magma chemistry is low in silica but enriched in sodium and potassium. The Pakawau area of Golden Bay is known for complex igneous and metamorphic geology, making this specimen a valuable regional reference.

80 x 73 x 43mm

219g