Nepheline pegmatite

Overview and images of pegmatite as a rock type are here: Pegmatite

This pegmatite rock sample from Norway has a texture of a pegmatite (very coarse-grained igneous rock) but the composition is pretty unusual. There are small amount of pink K-feldspar that is the dominant component of granitic rocks but here much more dominant seems to be gray nepheline which is a feldspathoid group mineral. Feldspathoids form when there is not enough silica to form feldspars, let alone quartz which is entirely absent.

Similar rocks are often described as syenites but this is not correct because the feldspathoid/feldspar ratio is too large. This rock sample should be named foidolite according to the QAPF diagram which is commonly used to classify plutonic rocks. Even more precise term is nephelinolite because the dominant feldspathoid is nepheline.

Other notable minerals besides nepheline and K-feldspar are black hornblende, dark metallic gray magnetite, and yellowish brown wöhlerite. Wöhlerite is a pretty rare silicate mineral that occurs in silica undersaturated rocks like the one above.

Pegmatitic igneous rock from Tredalen near Larvik. Gray is nepheline, yellowish brown is wöhlerite, black is hornblende, pink is K-feldspar, and gray is magnetite. The width of the specimen 14 cm.