SAMARSKITE, GADOLONITE, ALLANITE,
FERGUSONITE, POLYCRASE,
AND EUXENITE
The
species above named form a group of black, heavy minerals, with pitchy
or sub-metallic luster, which are occasionally cut when a brilliant
black gem is desired. They are peculiar in their composition in that
they are salts of the rare earths, yttrium, cerium, tungsten niobium,
etc. They are therefore often known as rare earth minerals. They have a
hardness of 5-6, and a specific gravity of 5-6. The latter is
sufficient to distinguish them from any other of the black minerals
used in jewelry, such as jet and obsidian, the difference being at once
noticeable on taking one of either in the hand. Their color being a
rich velvet black, and their luster brilliant, they are superior in
appearance to the more extensively used black minerals, and should have
a wider vogue. Samarskite is perhaps the richest in color and luster of
any of the series, this being a deep velvety black. The minerals are
found in this country chiefly in North Carolina, although allanite is
obtained also in Virginia and Texas. In Europe they are found in Norway
and the Ural Mountains.
