takes a polish which would be perfect if it was not resinous, and which
it loses in the course of time. Its colour, quite different from that
of the plasma, which is rather olive, is of a decidedly emerald green.
and rare are the pieces of pure prase, as this stone is always mixed
and marked with lime, and its internal crystallization is not
homogeneous or perfect. When it presents the appearance of a regular
crystal it takes the form of a prism or pyramid, having six faces of
medium size ; its external surface is rough and not very bright, but
the breakage is scaly, concave, and of a vitreous light.
The prase in block is often formed of pieces stuck together, whose faces, somewhat rough, are obliquely lined.
This mineral, which has a specific gravity of 2*67, yields on being analysed