Roscoelite:
A Silicate of Aluminium and Potassium. A rare green mica, a variety of
Muscovite, occurring in minute scales, sometimes arranged in fan-like
and stellated groups. It is found intimately associated with native
Gold in California and is used as an ore of Vanadium of which it
contains from 20 to 2Sfc It was named after the English Chemist, Roscoe.
Roselite: A
native Arsenate of Cobalt. It occurs in small crystals in druses of
crystals, and in spherical aggregates, with color varying from light
red to dark rose-red. It
it found in Schneeberg, Saxony and in Baden, and is named after
the German Naturalist, Rose.
Rose Quartz: A cloudy, pink variety of Quartz. This attractive stone is used to some extent in artistic jewelry.
Rubellite: A pink or red variety of Tourmaline. The pure transparent stones are used as gems.
Ruby: A
ruby-red Corundum. A precious stone with a red color, verging to
violet, the most valuable being know to lapidaries as "Pigeon Blood"
red. It occurs in crystals in Siam, Ceylon, Brazil, Hindustan,
Australia, Mandalay, and Burma from whence come the finest specimens.
It ranks next to the Diamond in hardness, and is one of the most
valuable of gem stones. A Ruby weighing 304 carats was reported to have
been found near Mandalay.
There
are two kinds of Rubies, the Oriental and the Spinel, the former being
distinguished from the latter by color and crystallization. The Spinel
Ruby is bright red in color, due to the presence of chromium oxide, and
is not doubly refracting or pleochroic like the genuine Ruby. (See
Corundum.)
Rutile: Titanium
Dioxide. Titanium 60%. This mineral is one of the oxides of the
comparatively rare element Titanium, occurring commonly in dark brown
opaque masses, in brilliant black crystals, and sometimes as fine
hair-like needles penetrating quartz. Twinning is common and often
repeated, producing elbow-shaped groups or wheel-shaped aggregates. In
color it is reddish-brown, yellowish-brown, black or bluish by
reflected light and deep red by transmitted light.
It
is used in the manufacture of the alloy ferro-titanium, added to steel
to increase the strength; in the manufacture of arc lights and the
filaments in incandescent lamps. It is also used in small quantities
to impart a yellow color to porcelain and an ivory tint to artificial
teeth.
