#magma

• 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.
• Akermanite — A mineral belonging to the melilite group, consisting of a complex calcium and magnesium silicate with the chemical formula Ca2MgSi2O7; it crystallizes in the tetragonal system and frequently occurs in silica-poor effusive igneous rocks, in contact-metamorphosed limestones, or as a major structural component in industrial metallurgical slags. This high-temperature mineral forms a continuous isomorphous series with gehlenite, being utilized in petrological studies to determine the thermodynamic conditions of magma solidification.
• 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.
• 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.
• 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.
• Allotriomorphism — A property, state, or structural phenomenon characteristic of certain minerals or igneous rocks, consisting of the development of crystals lacking their own geometric faces or a native regular outer shape. This mineralogical process occurs when crystal growth is mechanically constrained and limited by the remaining free spaces between other mineral components solidified previously within the mass of the same magmatic melt.
• Amphibole — A generic name for an extensive group of inosilicate minerals with a monoclinic or orthorhombic crystalline structure, composed of double chains of silicon dioxide tetrahedra. This structural group, which includes hornblende, actinolite, and tremolite, typically contains iron, magnesium, calcium, and sodium ions, being an essential constituent of many dark-colored igneous and metamorphic rocks.
• Anatexis — A deep geological process of partial or total melting of pre-existing rocks within the lower crust (metamorphic or igneous) under the action of extremely high temperatures and pressures. Representing the ultimate stage of regional metamorphism (ultrametamorphism), anatexis leads to the formation of secondary granitic magmas and mixed rocks called migmatites, playing a fundamental role in the recycling and structural evolution of the lithosphere.
• Inclusion — A fragment of an older rock or a pre-existing crystal incorporated into the mass of an igneous or metamorphic rock during the consolidation of magma; a mineral inclusion captured within a structurally different host medium. As an adjective, it describes a petrographic texture marked by the presence of such captive minerals or elements.
• 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.
• Andesite — An effusive (volcanic) igneous rock with a microlitic or porphyritic texture, gray, brown, or greenish in color, mainly composed of plagioclase feldspar (such as andesine) and ferromagnesian minerals (amphiboles, pyroxenes, or biotite). It has a wide distribution in eruption areas and is intensely used in construction as dimension stone, paving, gravel, or structural aggregate due to its hardness.
• Andesitic — Belonging to andesite, relating to andesite, or having the composition, structure, and characteristics specific to this effusive igneous rock. In petrography, it describes magmas, lavas, tuffs, or volcanic flows with an intermediate silica content, characteristic of tectonic subduction zones.
• Annite — A rare silicate mineral, specifically an iron-rich endmember of the biotite mica group containing trivalent iron and potassium, officially recognized in international mineralogical classifications as annite. In geology, its presence within magmatic or metamorphic rocks provides crucial insights into pressure, temperature, and partial melting conditions within the Earth's crust.
• 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.
• Anorthosite — A phaneritic plutonic igneous rock composed almost exclusively (over ninety percent) of calcium-rich plagioclase feldspar. It holds exceptional geological importance, forming ancient Precambrian magmatic massifs on Earth and constituting the primary structural component of the heavily cratered lunar highlands (the early lunar crust).