felsic

adj

1. Enriched in minerals predominantly composed of the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.

   “Much of the southern half of the southeastern body is a mafic syenite, slightly more felsic than the shonkinite.”

   “Within comagmatic suites, successively younger granitoids are commonly, but not invariably, more felsic, representing progressively lower temperature mineral assemblages.”

   “The Claret Creek Supersuite granites are a little more felsic (65-77% SiO₂), and are chemically distinctive, having higher Al₂O₃, CaO, Na₂O and Sr, and lower K₂O, Rb, Th and U than the granites of the Almaden Supersuite.”

noun

1. A rock with such properties.

   “The central part of this nepheline syenite is very white felsics with black mafics in it. The entire area contains many nepheline-bearing dike rocks, but almost all are gray or pink or even red due to the color in the felsics.”

   “There are also calcalkaline felsics that have highly enriched LREE^([light rare-earth element]) patterns with lower overall abundances.”