The
hauyna is not much known. It is used in making rings, buckles, and
ear-rings, being cut like the idocrasium, and will be always prized on
account of its rarity.
XLVIII.
IDOCRASIUM.
This mineral
is almost always found crystallized in the form of a prism of four
sides terminated by four pyramids, and also sometimes in pebbles.
Its
cleavage is parallel to all the sides of the prism. It is opaque and
transparent ; has double refraction ; its light is between vitreous and
resinous. Its breakage is concave. All its crystals are striped
lengthways.
It is generally yellowish green, brown, or orange yellow, and sometimes black and blue.
It
marks white glass and felspar, but can be marked by the topaz. It
yields a white powder, and its specific gravity is from 3'4 to 3*8.
It. melts under the action of the blow-pipe into a dark glass. It is
composed, like the garnet, of silex, alumina, lime, and some oxide of
iron and manganese. Idocrasium is found in various geological
positions, amongst volcanic and primitive rocks. "When first discovered
at Yesuvius it was distinguished by the name of volcanic scoria, brown
jacinth, volcanic chrysolite, and Vesuvian gem ; but found afterwards
in the cavities of the windings on the Alps, on AEtna,, in Sweden, Norway, Spain, and
