The silicate tetrahedron (SiO4
) is the basic
chemical unit of all silicate minerals. The number
of tetrahedra in the crystal structure and how
they are arranged determine how a silicate
mineral is classified.
Serpentine silicates are classified as ‘sheet
silicates’ because the tetrahedra are arranged
to form sheets. Amphibole silicates are classified
as ‘chain silicates’ because the tetrahedra
are arranged to form a double chain of two rows
aligned side by side. Magnesium is coordinated
with the oxygen atom in serpentine silicates. In
amphibole silicates, cationic elements such as
aluminium, calcium, iron, magnesium, potassium,
and sodium are attached to the tetrahedra.
Amphiboles are distinguished from one another
by their chemical composition. The chemical
formulas of asbestos minerals are idealized. In