Hydrolysis

From GeoClasses

Hydrolysis is the chemical reaction by which acids in water break down silicates. Silicate minerals are transformed into clays.

Clays from Wikipedia

• Clay is a generic term for an aggregate of hydrous silicate particles less than 2 μm (micrometres) in diameter. Clay consists of a variety of phyllosilicate minerals rich in silicon and aluminium oxides and hydroxides which include variable amounts of structural water. Clays are generally formed by the chemical weathering of silicate-bearing rocks by carbonic acid, but some are formed by hydrothermal activity. Clays are distinguished from other small particles present in soils such as silt by their small size, flake or layered shape, affinity for water and high plasticity index.

As you already know, mafic minerals are more susceptible to weathering than felsic minerals. Quartz, for example is highly resistant to hydrolysis, which is why when everything else is weathered away only quartz remains, which is why most of the sand on the beaches on in sand dunes is made of quartz.