#chemical composition

• Allophane — An amorphous or poorly crystalline hydrated aluminum silicate mineral, often associated with the weathering of volcanic rocks and ash deposits in humid environments. This structural compound exhibits a variable chemical composition and a gelatinous or vitreous texture, holding significant importance in soil science due to its high cation exchange capacity and phosphate-fixing ability in andosols.
• Alunite — A natural mineral from the class of hydrated sulfates, structurally composed of a basic aluminum and potassium sulfate, having the chemical formula KAl3(SO4)2(OH)6. Historically called alumstone, it occurs as granular, fibrous masses or white, grayish, or reddish rhombohedral crystals, used on an industrial scale for extracting alum and aluminum.
• Alunite — A formal variant or structural feminine adaptation of the term 'alunit', sometimes used in older technical literature or mining jargon to denote alumstone; a sedimentary or hydrothermal rock composed predominantly of this mineral. This compound represents an important natural source of hydrated aluminum and potassium sulfates, processed industrially for its astringent qualities.
• Alvanite — A rare natural mineral from the hydrated vanadate class, structurally composed of a hydrated aluminum and zinc vanadate, having the chemical formula Al3(VO4)(OH)6·2H2O or related. It occurs as microcrystalline aggregates, crusts, or rosettes of a pinkish-yellow, white, or grayish color, found in the oxidation zones of uranium and vanadium deposits.
• Alvanite — A formal variant or structural feminine adaptation of the term 'alvanit', sometimes used in older technical literature or mineralogical translations; a rock or mineral aggregate composed predominantly of this hydrated vanadate. It represents a compound of purely scientific and collecting interest due to its extreme rarity in the Earth's crust.
• Argentite — A mineral from the sulfide class, composed of silver sulfide with the chemical formula Ag2S, structurally stable only at temperatures above 173°C. At ambient temperatures, it transforms through pseudomorphosis into acanthite (its stable monoclinic modification), while retaining its initial outer cubic form. Industrially, it is an extremely important silver ore, featuring a dark grey to black color, a bright metallic luster, and high density.
• Astrospectroscopy — An elite branch of practical astrophysics dealing with the photography, digital recording, and structural analysis of the electromagnetic radiation spectra emitted or absorbed by celestial bodies. By decomposing stellar light using prisms or diffraction gratings attached to telescopes, astrospectroscopy enables the determination of chemical composition, temperature, pressure, radial velocity, and magnetic field strength of objects in the universe.