Euclase
is a rare mineral, resembling beryl in color and hardness, and like it
a silicate of glucina and alumina. It differs from beryl, however, in
containing water in its composition, in being monoclinic in
crystallization, and in having higher specific gravity. The percentage
composition of euclase is: Silica 41.3, alumina 35.2, glucina 17.3, and
water 6.2. Its specific gravity is 3.05-3.10. It barely fuses before
the blowpipe, and is not attacked by acids. It has a vitreous luster,
which becomes more brilliant on polishing a surface. The cut stones are
made from transparent crystals, which range from colorless to blue and
green, the latter resembling Russian topaz and aquamarine. Brazil and
the Ural Mountains furnish practically all the euclase thus far known,
and this in but small quantity. The Brazilian euclase is found at Boa
Vista, in the province of Minas Geraes, in the same locality with
yellow topaz. It occurs in nests in quartz veins which penetrate the
schists of the region. The crystals found in the Urals are larger, one
three inches in length being known. Euclase is also found in the
auriferous gravels of the Sanarka River in the Government of Orenburg,
Russia, chrysoberyl and topaz being accompanying minerals. Euclase
possesses a strong cleavage, which gives it its name, and makes it
somewhat difficult to cut. On account of the rarity of the mineral
good stones command a high price.
