one of a group of minerals known by the group-name of Pyroxenes, which
are metasilicates of calcium, magnesium, and iron. Of the numerous
varieties of Augite we are only concerned with one, Diopside, and the
description will be confined to that.
which is also known as Malacolite, Alalite, and Mussite, occurs in
green, or rarely grey, to white crystals usually attached in groups
(Fig. 17). The tint of green varies from very pale to very dark. The
crystals are transparent to translucent, and of a high vitreous lustre.
They are doubly refracting, but show only very slight dichroism, even
in the specimens possessing a deep colour. The specific gravity varies
from 3"2 to 3-4, being greater in the deeper coloured
varieties. Diopside is a brittle mineral. Its hardness is equal to 6,
and it has a well-marked cleavage parallel to the faces of the rhombic
prism. It crystallises in the monosymmetric system, and the usual habit
of the crystal is prismatic, with a well-marked oblique termination.
The prism faces are striated longitudinally. The prism is composed of a
right-angled form, whose solid edges are truncated by the faces of the
rhombic prism. The crystals are always attached at one end, and are
often in groups. Twin crystals are often seen. It occurs in cavities,