Phyllosilicate
A sheet-structured silicate, such as serpentine or clay, formed in meteorites when water altered the rock.
Phyllosilicates are silicate minerals built from stacked sheets of silicon–oxygen tetrahedra, with water or hydroxyl groups held in their structures. In meteorites the main types are serpentine-group minerals and smectite clays such as saponite, often finely intergrown and mixed with other alteration products. They dominate the matrix of CI and CM carbonaceous chondrites and occur in smaller amounts in other groups.
They are direct evidence of aqueous alteration: liquid water, released as ice melted inside parent asteroids, reacted with anhydrous silicates, metal and glass within the first few million years of the Solar System. Their abundance and type help define petrologic types 1 and 2 and the degree of alteration, and they lock up much of the water carried by carbonaceous chondrites. Orgueil, a CI chondrite that fell in France in 1864, is rich in clays, while Murchison, which fell in Australia in 1969, and Winchcombe, which fell in England in 2021, are CM chondrites with abundant serpentine. Samples returned from asteroids Ryugu and Bennu are also rich in phyllosilicates.
Phyllosilicates are too fine-grained to identify by eye. X-ray diffraction, transmission electron microscopy and infrared spectroscopy are used to characterise them.
Related terms
Level: Expert Advanced