Talc:
A soft unctuous mineral consisting of Silicate of Magnesium, mixed with
small quantities of Potash, Alumina, Oxide of Iron, and water. It is
used for many things such as tailor's
chalk, slate pencils, etc., but most extensively in toilet powders. A
massive variety, soapstone, is used in switchboards, and made into
hearthstones, (see Steatite).
Tantalite: A
nearly pure Tantalate. The name was given from the mythic "Tantalus" in
playful allusion to the tantalizing difficulties encountered in
attempts to make a
solution of this mineral in acids. The name was afterwards extended
to the American variety, Columbite.
It occurs in crystals, and massive, iron-black, grayish and brownish-black in color.
This
mineral is the source of the rare metallic element, Tantalum, which is
employed in the manufacture of filaments for certain types of electric
lamps. Since however, about 20,000 filaments may be made from a single
pound of the metal, the market for tantalum ores is very limited.
It is found in Finland, Sweden; also in North Carolina and Alabama.
Tenorite: Cupric Oxide. Copper 80%, Oxygen 20%. (see Melaconite).
Tephroite: Manganese
Orthosilicate. This mineral, occurring usually in crystalline masses,
is brown, gray or rose in color and transparent or translucent. It is
strongly
pleochroic in reddish, brownish and greenish-blue tints. It occurs in
Sweden, and at Sterling Hill and Franklin New Jersey, and is of
little commercial value.
Tetrahedrite:
A Sulphantimonite of Copper. Sulphur 23%, Copper 52%, Antimony 25%.
Known also as "gray copper" by reason of its color in massive
specimens. It occurs also in crystals, massive, and granular, with
color flint-gray and iron-black; sometimes cherry-red in thin splinters.
This mineral is found in many places associated with copper, lead and silver ores, and is mined for copper.
Thomsonite: Hydrous
Silicate of Calcium, Aluminium and Sodium. The composition varies. It
occurs columnar, structure radiated, spherical and closely compact;
rarely in crystals. In color it is snow-white, reddish, greenish and
brown. Transparent to translucent.
