Some of the slightly cloudy Ceylon sapphires, usually of greyish-blue colour, display when cut with a convex face a chatoyant luminosity, sometimes forming a luminous star of six rays, whence they are called "star sapphires".
The iodide, Co12, is produced by heating cobalt and iodine together, and forms a greyish-green mass which dissolves readily in water forming a red solution.
It varies in colour from greyish to bright yellow or greenish-brown, the first-named being the purest.
The wing-quills are brownish black, banded with mottled white, and those of the tail, except the middle pair, which are wholly greyish brown, are banded with mottled white at the base and the tip, but dark brown for the rest of their length.
Grisea is greyish in tint and produces a spherical egg with a spiky shell, which also is dropped into the mud.
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