Picture of Mica from geology.about.com

An introduction to igneous rocks – Part 2

Micas Of which there are two predominant varieties in igneous rocks – Biotite and Muscovite – are a group of phyllosilicates; the name in allusion to the method and ease of perfect cleavage of the mineral into exceedingly thin laminae. They are characteristic of a wide range of rock type. Biotite, the mafic variety, is…

Picture from: mii.org Fedspar microcline.

An introduction to igneous rocks – Part 1

What is an igneous rock? It’s hard, may be pale or nearly black, but what’s in it? This entry is aimed as a brief introduction to igneous mineralogy/petrology to the ‘beginners’ and it may be useful to have available a mineralogy and/or petrology text, see the ‘Books’ below the title bar. An igneous rock is…