Gneiss is a metamorphic rock that forms when granite or clay-rich rocks are transformed deep in the earth’s crust under high pressure and temperature. Its hallmark is a distinct banding (gneissic structure): alternating light and dark layers of different minerals.
Application
Gneiss is hard, durable and frost-resistant, so it is used as a natural stone:
- Paving — as setts, kerbs and slabs.
- Facade cladding — as polished or sawn panels.
- Floors and stairs — where wear resistance is wanted.
- Hydraulic works — as riprap for banks and dyke revetments.
The minerals that make up gneiss are mainly feldspar, quartz and mica — the same as in granite. The difference is the layered, oriented structure formed during metamorphism. Because of this banding, gneiss splits more easily along the layers than granite does. This directional sensitivity is taken into account when it is used as facing or flooring.
Related terms
- Natural stone
- Granite
- Metamorphic rock
- Slate
- Bluestone
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