#igneous rock

• 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.
• Aphanite — An igneous rock (volcanic or subvolcanic) featuring an extremely fine-grained, microcrystalline, or glassy texture, where the component crystals are so small that they cannot be distinguished with the naked eye, requiring an optical microscope for identification. As an adjective, it describes the specific texture of these rocks (such as basalt or andesite), resulting from the rapid cooling of magma at the Earth's surface.
• Aphanitic — Pertaining to or having the characteristics of an aphanite; a term used to describe the texture of igneous rocks whose crystalline components are of microscopic or submicroscopic dimensions, making them indistinguishable to the naked eye. This extremely fine structural arrangement indicates a rapid solidification of magma or lava at or near the Earth's surface, a process that prevented the growth of large crystals.
• Aphyric — A specialized geological term used to describe an igneous or volcanic rock with an extremely fine-grained, microcrystalline, or glassy texture, completely lacking phenocrysts. Aphyric rocks form through the rapid cooling of lava at the Earth's surface.
• Alkalic — Containing alkali; having basic or alkaline properties; alkaline. In geology and petrography, the term describes igneous rocks or minerals rich in alkali metals (such as sodium and potassium), characterized by a specific chemical composition that influences the structure and evolution of crustal melts.
• Aldur — A scientific term or rare variant designating a specific type of granular mineral aggregate or a microcrystalline structural variety found in ancient igneous rocks. In a broader sense, the word is analyzed in comparative petrology studies to describe silicate formations resistant to thermal erosion, which develop under extreme pressure conditions in the Earth's crust.
• Allotriomorphic — Relating to minerals or crystalline components of an igneous rock: not presenting its own geometric faces or a regular native external shape, because its structural development was limited and constrained by the free spaces remaining between crystals formed earlier during magma solidification.
• 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.
• Andesine — A mineral belonging to the plagioclase feldspar group, consisting of an isomorphic mixture of albite and anorthite in determined proportions, being a natural silicate of aluminum, calcium, and sodium. It crystallizes in the triclinic system and represents an essential and diagnostic component in the structure of intermediate igneous rocks, its name being linked to its abundant occurrence in the Andes mountain range.
• Autometamorphism — A geological process of mineralogical transformation and alteration of an igneous rock, caused in the final stages of its consolidation by its own residual gases, water vapor, and hydrothermal solutions released during magma cooling. This phenomenon transforms unstable primary minerals into new secondary assemblages (such as serpentinization or chloritization of basalts) without the input of external tectonic pressures or temperatures.