#feldspar

• Adamellite — A coarse-grained plutonic igneous rock, considered a specific variety of granite or quartz monzonite, in which potassium feldspar and plagioclase feldspar (especially oligoclase or andesine) are present in approximately equal amounts. This crystalline rock also contains abundant quartz and ferromagnesian minerals such as biotite or hornblende, commonly found in ancient mountain massifs.
• Alfel — A rare mineralogical term used to describe a specific variety of feldspar or a microcrystalline structure associated with native silicates. In older geological papers, the word referred to structural compounds of magmatic rocks, acting as a technical neologism systematically tracking granular textures.
• Aluminosilicate — A complex mineral within the silicate class (representing a large portion of the Earth's crust, such as feldspars, zeolites, and micas) in whose crystalline frameworks part of the silicon atoms are replaced by aluminum atoms bound to oxygen.
• Alumosilicate — A terminological or spelling variant (influenced by German and Russian nomenclatures) for 'aluminosilicat' (aluminosilicate); a complex mineral within the silicate class in whose crystalline frameworks part of the silicon atoms are replaced by aluminum atoms.
• Amazonite — A green to bluish-green variety of microcline feldspar, crystallizing in the triclinic system, widely used as a semi-precious ornamental gemstone. Its unique color and vitreous luster are structurally caused by microscopic trace amounts of lead and water within the crystal lattice.
• Andesine — A mineral belonging to the silicate class, specifically an intermediate variety of plagioclase feldspar, structurally defined by a specific chemical ratio between albite and anorthite (between 30% and 50% anorthite). It is a common constituent of intermediate igneous rocks, such as andesites and diorites, receiving its name from the Andes Mountains, where it was initially identified and abundantly described.
• Anorthite — A mineral belonging to the silicate class, representing the pure calcium endmember of the plagioclase feldspar isomorphic series (calcium aluminum silicate). It crystallizes in the triclinic system, features a white, grayish, or reddish color, and is a common structural constituent in basic and ultrabasic igneous rocks (such as gabbros and basalts), as well as in some metamorphic rocks or meteoritic materials.
• Argillize — To transform or become transformed into clay through chemical and hydrothermal alteration processes of preexisting minerals (especially feldspars) under the action of atmospheric agents or endogenous solutions. This mineralogical phenomenon alters the original structure of the silicate rock, leading to the accumulation of clay minerals and a decrease in the mechanical cohesion of the rock massif.