Earth Sciences 1022A/B Lecture Notes - Lecture 4: Silicate Minerals, Mafic, Ionic Bonding

• School: Western University
• Department: Earth Sciences
• Course: Earth Sciences 1022A/B
• Professor: Molnar

Document Summary

Most igneous rocks are principally made of silicate minerals (although other types of minerals do occur in smaller quantities). As their name implies, silicate minerals all contain the substance called silica. Silica is a complex ion made of 1 silicon atom bonded to 4 oxygen atoms, The silica unit occurs in the form of a tetrahedron. Common minerals of igneous rocks: ferromagnesian silicate minerals. Ferromagnesian silicates: iron and/or magnesium heavy ions (mg2+, fe2+, Fe3+) are ionically bonded with silica units (+ other additional ions in some varieties) tend to be dark-coloured. Common minerals of igneous rocks: non-ferromagnesian silicates, part 1. Non-ferromagnesian silicates: tend to be light coloured. Feldspars: silica framework plus light cations (k+, na+, ca2+) Na-rich plagioclase is light coloured; ca-rich plagioclase is dark coloured. Both minerals have two sets of cleavage meeting at 90o, reflecting the same pattern of bonding weakness within the crystal structure of the feldspar mineral group.