The 'Oriental Topaz" is yellow sapphire, and "False Topaz" is yellow quartz.
Torbernite: Hydrous
Phosphate of Uranium and Copper. Uranium Trioxide 61.2%, Copper 8.4%.
Its crystals occur in small square tables that may be very thin or
moderately thick; and in foliated and micaceous masses, emerald-green
or leek-green to apple-green in color. Transparent to translucent. It
is strongly pleochroic in green and blue.
Torbernite
is one of the ores of Uranium from which the element, Radium, is
extracted. It occurs in Saxony, Bohemia; at Cornwall, England, and at
Mohave, Arizona, (see Radium).
Touchstone: A
velvety-black siliceous rock or flinty-quartz, used on account of its
hardness and black color, for trying the purity of the precious metals.
The color left on the stone after rubbing the metal across it,
indicates to the experienced eye, the amount of alloy in the metal. It
is used in conjunction with the touching-needles for ascertaining the
purity of gold and silver. It is also called Basanite or Lydian Stone
and is found in Quartz localities.
Tourmaline: A complex Silicate of Boron and Aluminium. This mineral
is of great scientific interest because of its complex
crystallization, its handsome crystals, and the physical properties
which it exhibits so beautifully. Tourmaline offers an example of a
semi-precious stone which is steadily growing in popularity for all
kinds of jewelry. There is a wide range of colors, practically all
colors of the rainbow: blue, green, red, blue, black, brownish, violet,
pink, honey-yellow, and colorless. Some specimens are red internally
and green externally, while others are red at one extremity and green,
blue or black at the other. The pink or red variety is known as
Rubellite, and the blue or blue-black, as Indicolite.
The
name Turmalin, from Turamali in Cingalese, was introduced into Holland
in 1 703 with a lot of gems from Ceylon. Because of its property of
attracting the ashes of burning peat, the Hollanders gave it the name
of Aschen-trecker or ash-drawer. The name Tourmaline was not commonly
used by mineralogists until a much later period. Tourmaline is
magnetic, becomes electrified by friction, and like other hemimorphic
substances is strongly pyroelectric. Prisms of Tourmaline possess such
powerful electric properties that they are used in polarizing
apparatus. The darker varieties are used in optical instruments.
