Finally,
the chrysolite of Spain crystallizes in hexa-hedral prisms, which are
flattened at the edges and terminated at the two poles by cupolas
having six facets. This Iberian species is a phosphate of lime, and is
softer than all the others.
Volcanic
earths, lava and basalts, often contain irregular grains which have
all the characteristics of the chrysolite ; nevertheless it is thought
to be nothing but coloured lava, such as is found at Vesuvius.
All these substances are cut on a leaden wheel, slightly spread with emery, and then polished on the copper-mill.
The
gem which we now call chrysolite was well known to, and must have been
prized by the ancients ; as I have had the opportunity of seeing some,
set in gold and very well preserved, and I even possessed some,
engraved in the best period of ancient art. Nevertheless, we shall
perhaps always remain ignorant of the name which that stone then had,
as also of the places where it was procured.
