berthierine

Berthierine is a mineral belonging to the serpentine group. It is a phyllosilicate mineral with the chemical formula Fe2+3-xAl2x(Si2-xAlx)O5(OH)4, where x is typically around 0.3. It is characterized by its greenish color, often appearing as flaky or earthy masses. Berthierine is a secondary mineral, meaning it forms through the alteration of other minerals, particularly those rich in iron and aluminum. It is commonly found in hydrothermal veins and in metamorphosed sedimentary rocks, especially iron formations. Its structure is similar to that of kaolinite, with layers of silica tetrahedra and alumina octahedra, but with iron substituting for some of the aluminum in the octahedral layer. The presence of ferrous iron (Fe2+) is a defining characteristic. Berthierine can be difficult to distinguish from other serpentine minerals like chamosite without detailed mineralogical analysis. It is named after the French chemist Pierre Berthier.