Ultrabasic

A rock which contains mainly ferro-magnesium minerals and feldspars with the virtual exclusion of quartz.
Found on http://www.encyclo.co.uk/local/20206

Ultrabasic

(of igneous rocks) containing less than 45% silica
Found on https://www.encyclo.co.uk/local/20501

ultrabasic

Describing an igneous rock containing magnesium and iron with a very low percentage of silica, less than 45%.
Found on http://www.encyclo.co.uk/local/22291
No exact match found