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Phonolite

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Phonolite

Phonolite is a volcanic rock. It was originally "Klingstein" in German on account of the sound emitted when it was struck by a hammer. It consists mainly of nepheline and alkali feldspar (sanidine or anorthoclase). Other minerals occuring in phonolite are soda-pyroxenes, soda-amphiboles, leucite, analcime and sodalite-group minerals (sodalite, nosean, hauyne). It is the volcanic equivalent of nepheline syenite.

Phonolite in hand specimen
click to enlarge click to enlarge   Phonolite is grey to dark green, usually with a porpyritic texture and a greasy lustre due to the presence of nepheline, which is also called elaeolite.
Left: phonolite, Right: leucitophyre

Phonolite under the polarizing microscope
Nicols //
click to enlarge
Nicols X
click to enlarge
 

Phonolite
Sa: sanidine, Ne: nepheline
Marangudzi, Zimbabwe

click to enlarge click to enlarge   Phonolite
Ne: nepheline
Comoro Islands, Indian Ocean
click to enlarge click to enlarge   Leucite phonolite
Lct: leucite, Ne: nepheline
Eifel, Germany
click to enlarge click to enlarge   Nosean leucite phonolite
Lct: leucite, Nsn: nosean
Laacher See, Germany

Pictures are taken from:
The Hamlyn Guide to Minerals, Rocks and Fossils (W.R. Hamilton, A.R. Wooley and A.C. Bishop)
Atlas of Igneous Rocks and their Textures (W.S. MacKenzie, C.H. Donaldson and C. Guilford)
A Colour Atlas of Rocks and Minerals in Thin Section (W.S. MacKenzie and A.E. Adams)


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