#diagenesis

• Aleurolite — A consolidated detrital sedimentary rock formed through the cementation and diagenesis of aleurite (fine mineral dust, chiefly quartzous). The dimensions of its component grains are intermediate between those of sandstones and argillites, ranging from 0.002 to 0.06 millimeters. It often exhibits fine stratification and is used in geology to reconstruct ancient fossil or lacustrine sedimentary environments.
• Anadiagenesis — An intermediate or deep stage within the general process of diagenesis, characterized by intense structural physicochemical transformations of sediments buried at great depths under increased temperatures and pressures, without reaching metamorphism. This phenomenon involves the recrystallization of clay minerals, massive compaction, deep dehydration, and cementation of interstitial fluids, leading to the definitive lithification of sedimentary 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.
• Argillite — A compact argillaceous sedimentary rock, structurally formed through the diagenesis and deep cementation of clay muds, characterized by a higher hardness than simple clay and by the absence of fissility or the ability to split into thin sheets (unlike clay shales). In a geological sense, argillite represents an intermediate stage of metamorphism between soft pelitic sedimentary rocks and crystalline clay shales.
• 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.