#minerals

• Alaite — A rare mineral belonging to the arsenate class, with a complex structural nature, appearing as microscopic crystalline aggregates or efflorescent crusts; a natural chemical compound containing arsenic and hydrated copper, occasionally found in the oxidation zones of polymetallic deposits. This mineral is of particular interest to collectors and geological researchers due to its rarity and specific formation conditions.
• 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.
• Allanite — A mineral belonging to the epidote group, black, brown, or gray in color, with a resinous or submetallic luster, containing significant percentages of rare-earth elements (cerium, lanthanum, neodymium, yttrium), alongside traces of thorium or uranium, which give it a weakly radioactive nature. It crystallizes in the monoclinic system and occurs as an accessory mineral in igneous (granites, pegmatites) and metamorphic rocks.
• Anchimetamorphism — A geological process of incipient, very low-grade metamorphism that marks the transition between diagenesis (sediment consolidation) and regional metamorphism proper (greenschist facies); it occurs at relatively low temperatures and pressures, causing partial recrystallization of clay minerals without completely destroying the original sedimentary structures.
• Andalusite — A structural mineral consisting of aluminum silicate that crystallizes in the orthorhombic system, being characteristic of metamorphic rocks formed under low pressures and medium to high temperatures. Due to its exceptional thermal resistance and high melting point, andalusite is widely used in industry as a refractory material for lining metallurgical furnaces, while its transparent and colored varieties are sometimes used as gemstones in jewelry.
• Andalusite — A linguistic variant or synonymous regional form of the standard term 'andaluzit', designating the natural aluminum silicate that crystallizes in the orthorhombic system. It is sometimes used in older geological treatises or technical translations to describe the rock or refractory mineral mass composed predominantly of this crystallized silicate type.
• 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.
• Ardealite — A very rare secondary phosphate mineral, structurally composed of hydrated calcium phosphate-sulfate, with the chemical formula Ca2(PO4)(SO4)·4H2O. It typically forms as an alteration product in cave guano deposits through the reaction of acidic phosphate solutions with surrounding limestone, first discovered and described in 1932 in the Cioclovina Cave in Hunedoara County, Romania, from which it derives its name structurally linked to the Ardeal region.
• Arsenical — Containing arsenic in its chemical structure, relating to arsenic, or derived directly from the compounds of this metalloid. In industrial and medical terms, it describes minerals, thermal mineral waters, industrial waste, or old pharmaceutical preparations that have variable proportions of arsenic in their composition, requiring special protective measures due to cumulative toxicity risks.
• Arseniferous — Containing or bearing arsenic in its structural composition; said of ores, rocks, geological strata, or groundwater in which arsenic is present as a stable chemical component or as a significant metallic impurity. The identification of arseniferous deposits is crucial in economic geology and environmental risk assessment, as processing these materials can release toxic substances into the surrounding environment.
• Arsenolite — A rare mineral composed of arsenic trioxide (As2O3), formed by the oxidation of other arsenic-bearing minerals in the upper zones of ore deposits. Its crystals are usually cubic or octahedral, white, gray, or yellowish in color, and are characterized by a relatively high water solubility and extreme toxicity.
• Authigenic — Said of minerals or sedimentary components that formed directly in situ, within the sediment or host rock, through processes of chemical precipitation, recrystallization, or diagenetic transformation, rather than being transported from elsewhere as pre-existing detrital material.
• Autunite — A mineral from the phosphate class, hydrated uranium and calcium phosphate, with the chemical formula Ca(UO2)2(PO4)2·10-12H2O, featuring a brilliant greenish-yellow color; it is a highly radioactive mineral that fluoresces under ultraviolet light, historically discovered in the Autun region (France) and used as a secondary uranium ore.