Dictionary of Geotourism

2020 Edition
| Editors: Anze Chen, Young Ng, Erkuang Zhang, Mingzhong Tian

Alkaline Rocks

Reference work entry
DOI: https://doi.org/10.1007/978-981-13-2538-0_37

Alkaline rocks are rocks that contain alkaline minerals (such as nepheline, aegirine and riebeckite). Alkaline rocks include ultrabasic, basic, intermediate and acidic rocks. The bulk rocks usually have low O2 contents but high alkaline (K2O+Na2O) contents. The rocks contain alkali feldspar, sodium pyroxene (such as aegirine and acmite augite), or sodium pyroxene (such as riebeckite and arfvedsonite). When the alkali content is high, the rock will not contain quartz but will contain feldspar minerals (such as nepheline, hauynite, and noselite). Typical examples are nepheline-syenite and phonolite. A rare type of nosean phonolite has been found at Niangniang (Empress) Mountain in Nanjing.

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