Larvikite

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Unpolished Larvikite rock.

Dark Larvikite with a polished surface.

Larvikite is probably a type of syenite, notable for the presence of handsome, thumbnail-sized crystals of feldspar, which are multiply-twinned on the micro-scale and shot through with small inclusions, giving its characteristic silver blue sheen (Schiller effect) on polished surfaces. Olivine can be present along with apatite, but there is rarely any free quartz. Usually titanium rich, with titanaugite and/or titanomagnetite present.

The name originates from the town of Larvik in Norway, where this type of igneous rock is found.

This rock is very popular in the High Street in the UK, for its high polish and spectacular reflections from its feldspars and is frequently found fronting the facades of banks. It is sometimes known informally as Blue Granite, although almost nothing of its mineralogical composition makes it granitic.