leucogranites

Leucogranites are pale, light-colored granitic rocks distinguished by a low abundance of dark ferromagnesian minerals and by high silica and alkali contents. The term emphasizes appearance and mineralogy rather than a strict petrographic class, and it is commonly applied to granites in which quartz and alkali feldspar dominate the mineral assemblage.

Mineralogy and texture: Leucogranites are typically quartz and alkali feldspar rich, with plagioclase present in variable amounts. Muscovite is common, while biotite and other ferromagnesian minerals are sparse or absent. Accessory minerals such as zircon, monazite, apatite, and sometimes tourmaline occur. The textures range from medium- to coarse-grained, and pegmatitic varieties are known in some bodies.

Formation and geologic setting: These rocks are commonly produced by high-degree partial melting (anatexis) of crustal rocks or by late-stage differentiation of granitic magmas within the continental crust. They are frequently associated with crustal thickening in orogenic belts and may intrude as plutons or form parts of larger granitic complexes in post-collision or active-margin settings.

Chemistry and classification: Leucogranites typically exhibit high silica content, often around 70–75 wt% SiO2, together with elevated alkalis. They are frequently peraluminous, reflecting a crustal source that contributes excess aluminum and minerals such as muscovite. In practice, leucogranite is a color-based descriptor that often correlates with crustal-derived, high-silica granitoids, and is sometimes linked with S-type granitoids, though coloration alone does not define a single geochemical class.