nonferromagnesian

Nonferromagnesian refers to silicate minerals that contain little to no iron (Fe) and magnesium (Mg). The term is used in geology and petrology to distinguish these minerals from ferromagnesian silicates, which are rich in Fe and Mg and typically dark-colored. Nonferromagnesian silicates are usually light in color and have lower densities than their ferromagnesian counterparts.

Common nonferromagnesian silicates include quartz (SiO2) and feldspars such as potassium feldspar (orthoclase, microcline) and plagioclase. Light-colored micas, notably muscovite, are also considered nonferromagnesian. Depending on the classification system, other light silicates able to occur with negligible Fe and Mg content may be included, but quartz, feldspars, and muscovite are among the principal examples in typical rock-formation contexts.

Geologically, rocks with a high proportion of nonferromagnesian silicates are typically felsic or silicic, characterized by high silica content and relatively low Fe and Mg. This mineral assemblage imparts light color, lower density, and specific melting and weathering behavior, distinguishing felsic rocks such as granite, granodiorite, and rhyolite from mafic and ultramafic rocks dominated by ferromagnesian minerals.

In metamorphic settings, nonferromagnesian minerals influence texture and stability, contributing to granoblastic or gneissic fabrics when subjected to appropriate temperatures and pressures. The contrast with ferromagnesian minerals remains a key basis for classifying rocks and interpreting geologic history.