basseinides

Basseinides are a group of minerals named after the historic Bassein region (present-day Vasai, near Mumbai), where they were first identified in hydrothermal veins within Deccan Traps basalts. The term was proposed in 2010 to classify a set of iron- and magnesium-rich silicate minerals that occur together with quartz and calcite. They are discussed in mineralogical literature as a distinct family within the broader silicate-oxide group.

Composition and structure: Basseinides form layered silicate structures containing octahedrally coordinated Fe2+ and Mg2+ with tetrahedral SiO4 units. The general formula is expressed as (Fe2+,Mg)2Si4O10(OH)2, with notable solid solution between Fe and Mg and occasional Mn substitution. Crystals are typically monoclinic, exhibiting platy to tabular habits; color ranges from olive-green to brown; luster is vitreous to resinous; hardness is about 5 on the Mohs scale.

Occurrence and formation: These minerals are characteristic of hydrothermal veins in basaltic rocks, especially in regions with prior serpentinization. They form at relatively low to moderate temperatures (roughly 150–300°C) under mildly reducing conditions, often alongside quartz, calcite, chlorite, and other silicate minerals.

Classification and status: Basseinides are regarded as a distinct mineral species within the broader silicate-oxide family. Their exact taxonomic position is under review, with some researchers grouping them with serpentine- or chlorite-family minerals pending further structural and geochemical data. Further discoveries may refine their distribution and relationships.

See also: Deccan Traps, Serpentine group, Chlorite group, Silicate minerals.

---