pleochroism.
Its crystals belong to the rhombic system. Good specimens, such as are
occasionally met with in Ceylon, show in different directions of the
crystal a soft lavender-blue, a greyish white, and a straw colour.*
lolite is frequently full of flaws and almost opaque ; its beautiful
change of colour is then very imperÂfectly seen. The hardness of iolite
is above 7 ; its specific gravity is 2'6 to 2-66. One hundred parts of iolite on an average contain about :
Crocidolite
Is,
or rather gives rise to, one of the minerals which lias been termed
cat's-eye. It occurs of three distinct colours—brownish yellow or gold
(tiger eye), indigo or greenish blue, and dull red. When cut en cabochon of
an oval form, with a high ridge, and with the longer diameter of the
oval at right angles to the direction of the fibres or filaments which
the mineral includes, crocidolite shows a good line of light and
presents a brilliant appearance. It always contains a chalcedonic base
; indeea the best specimens, which now come from Griqualand West, South
Africa, and have a hardness of nearly 7, and specific gravity of 2.8,
are essentially pseudomorphs after crocidolite, and not the unchanged
mineral itself, which is softer and heavier. This stone is related to
hornblende and asbestos, and has approximately this composition in 100
parts :
Bronzile
and Hypersthene are two other minerals, resembling crocidolite in their
metallic reflections, and consisting of silica, iron oxides, and
magnesia.
* Frontispiece, Fig. 5.
