Gneiss

The single most important thing I can teach you about gneiss is that its pronounced pretty much exactly like the word ‘nice’, meaning pleasant. Nys/Nise – a silent G.  

Gneiss is a metamorphic rock which is mainly composed of quartz, feldspar, and mica. It may contain other minerals such as amphibole, kyanite, cordierite, biotite, staurolite, or garnet.

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Information about Gneiss

Appearance

Gneiss is a metamorphic rock which is mainly composed of quartz, feldspar, and mica. It may contain other minerals such as amphibole, kyanite, cordierite, biotite, staurolite, or garnet.

It is often banded or layered.

Uses and History

Gneiss is sometimes used as a decorative rock, and has often been used as a building material around the world, and as construction aggregate.

Mineralogy

Chemistry
Gneiss is a metamorphic rock which is mainly composed of quartz, feldspar, and mica. It may contain other minerals such as amphibole or garnet. The composition does vary quite widely.
Colours and Variations
Often but not always banded. Banded specimens are generally dark and light.
Streak
White to grey
Luster
Generally dull to subvitreous, may differ.
Transparency
Opaque.
Fracture
Irregular to splintery.
Crystal habit
Often banded or layered; does not form crystals as it is a grainy rock made up of minerals.
Mohs hardness
Typically 6-7.
Fluorescence
Not typically, although may contain minerals which fluoresce.
Specific Gravity
Varies on composition.
Easiest testing method
Alternating bands is one quite easy visual method.

Hazards and Warnings

Generally non toxic.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

 

Translations

Arabic:

Hindi:

Portuguese:

  • Gnaisse

Bengali:

Indonesian:

Punjabi:

English:

  • gneiss

Italian:

Russian:

  • Гнейс

French:

Japanese:

  • グナイス

Spanish:

German:

  • Gneis

Korean:

  • 편마암

Thai:

  • ไนส์

Gujurati:

Mandarin Chinese:

  • 片麻岩

Urdu:

Further Reading / External Links