Lisandites

Lisandites are a category of sedimentary rocks described in parts of the geological literature as sand-rich lithologies that resemble sandstone but exhibit distinctive mineral and cement characteristics. They typically contain sand-sized grains dominated by quartz and feldspar, with smaller amounts of lithic fragments. Cementation is variable but often involves silica overgrowths or iron-oxide minerals, which can give the rock a reddish to brownish color and a relatively durable texture.

Petrographically, lisandites are characterized by a prominent sand-sized grain framework with noticeable proportions of feldspar and lithics compared with pure quartz arenites. The cementing materials contribute to cohesion and affect porosity and permeability. Their textures can preserve sedimentary structures such as cross-bedding, planar lamination, and grain-to-grain contacts that indicate depositional energy conditions during burial.

Depositional environments associated with lisandites include braided and meandering river systems, alluvial fans, and deltaic plains, where substantial sand supply and episodic energy fluctuations promote rapid sand deposition. Diagenetic processes, including cementation and compaction, modify initial porosity and permeability and may enhance resistance to erosion.

Occurrence and significance vary across basins and regions, with lisandites reported in several sedimentary sequences worldwide. They can serve as potential reservoir rocks in hydrocarbon systems or as aquifers where porosity remains adequate. Their study contributes to understanding sediment transport, depositional dynamics, and diagenetic pathways in sand-rich successions.

See also: Sandstone, Arkose, Wacke, Cementation, Sedimentary rock.