These are hydrous ferromagnesian silicate minerals and along with pyroxene constitutes about l/5th of all the known rocks.
Inosilicates characterised by double chain structure.
Hydrous silicates of Magnesium, Iron, Calcium, Aluminium as well as Alkali metals.
Some minerals of the group are distinctly orthorhombic, and monoclinic, others are triclinic in their crystallisation. [Accordingly each group shows different characteristics under microscope].
(a) Orthorhombic. (i) Anthophyllite (MgFe)7(Si40I1)(0H)2,.
Most of the members are greenish black in colour.
2 sets, perfect, prismatic (110),
6. Sp. Gravity:
2 5 to 3 5.
Contact twins are common.
(i) Green colour and commonly pleochroic.
(ii) Ref-index. High.
(iii) Interference colour.
Clinoamphiboles 10° to 20°.
(a) Amosite-Fibrous anthophyllite.
(b) Actinolite-Asbestos proper.
(c) Crocidolite-Fibrous riebeckitc.
(d) Chrysotile-Fibrous serpentine.
Fine grained tremolite-actinolite.
Mostly occur in metamorphic rocks and also in igneous rocks. Crocidolite occurs in highly siliceous metamorphic rocks.