What does a dark colored igneous rock indicate?

For coarser rocks Dark coloured igneous rocks indicate presence of mafic minerals as major rock constituents. Mafic minerals include olivine, pyroxenes and amphiboles. read more

For coarser rocks Dark coloured igneous rocks indicate presence of mafic minerals as major rock constituents. Mafic minerals include olivine, pyroxenes and amphiboles. These minerals are rich in magnesium and iron content which gives them dark colour. read more

Colour index: Colour index,, in igneous petrology, the sum of the volume percentages of the coloured, or dark, minerals contained by the rock. Volume percentages, accurate to within 1 percent, can be estimated under the microscope by using a point-counting technique over a plane section of the rock; volumes also read more

____ are minerals typically found in igneous rocks that have a high silica content, whereas ____ are minerals that are typically found in igneous rocks with a low silica content. read more

A porhyritic texture indicates that the rock or rock body: A) initially cooled slowly, then more rapidly. B) initially cooled rapidly, then more slowly. C) cooled slowly, becoming enriched in silica. D) cooled rapidly, composition staying the same. E) has a history too complex to make any of the above statements. read more