#petrography

• Ataxite — A structural type of iron meteorite (siderite) extremely rich in nickel (over 16%), characterized by the absence of Widmanstätten patterns when etched with acid. In a broad petrographic or structural sense, the term also describes an igneous rock or brecciated mineral mass with a completely irregular and unhomogeneous texture, formed by the chaotic mixing of distinct fragments.
• Augitite — An effusive, ultrabasic, and melanocratic igneous rock, completely lacking feldspars, composed primarily of large augite and magnetite crystals embedded in a glassy or microcrystalline basaltic groundmass. In structural geology, it represents a rare variety of volcanic pyroxenite.
• Autolith — Fragments of early igneous rock incorporated into a younger igneous rock mass, both originating from the same parent magma or deep magmatic chamber. Also known as cognate inclusions or autoliths, these petrographic structures represent portions crystallized at the beginning of the cooling process, which were later detached and engulfed by the remaining fluid magmatic flow, providing crucial data on the chemical evolution of the magmatic reservoir.
• 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.
• Bachelite — A rare mineral or a structural petrographic variety described in old geological reference works, sometimes used as a spelling variant for industrial bakelite or as a regional name for a certain type of compact sedimentary rock. In contemporary vocabulary, it is monitored to prevent confusion with bakelite (the plastic material), representing a strictly technical term within a narrow geological niche.
• Bafflestone texture — A type of autochthonous carbonate sedimentary rock (limestone), according to the revised Dunham classification (Embry and Klovan), where the original organic components (such as fan-shaped corals or calcareous algae) grew together during deposition, acting as baffles that slowed down water flow and trapped fine sediment.
• Bahamites — Granular marine limestone sedimentary deposits, consisting predominantly of oolites, bioclasts, skeletal fragments, and calcium carbonate aggregates, typical of warm, shallow, and agitated waters in tropical regions; named after the classic strata investigated on the Bahama Banks. Structurally, they describe a petrographic suite serving as a modern reference model for carbonate platforms.