SILICA. S4t 
smooth and shining globular, botryoidal masses, having a 
pearly lustre. 
Float Stone. A variety of opal having a porous and fibrous 
texture, and hence so light that it will float on water. It 
occurs in conecretionary or tuberose masses, which often 
have a nucleus of quartz. 
Tripolite, or Infusorial Harth. A white or grayish-white 
earth, made mainly of siliceous secretions of microscopic 
plants called Diatoms. Itforms beds of considerable extent, 
and often occurs beneath peat. It is used as a polishing 
powder ; also to mix with nitroglycerine and make dynamite ; 
and, owing to its poor conduction of heat, it is applied as a 
protection to steam boilers and pipes. 
Tabasheer is a siliceous aggregation found in the joints of 
the bamboo in India. - It contains several per cent. of water, 
and has nearly the appearance of hyalite. 
Diff. Infusibility before the blowpipe is the best charac- 
ter for distinguishing opal from pitchstone, pearistone, and 
other species it resembles. The absence of anything like 
cleavage or crystalline structure is another characteristic, 
Its inferior hardness and specific gravity separates 1t from 
quartz. 
Obs. Tyalite occurs sparingly at the Phillips ore bed, 
Putnam County, N. Y., and in Burke and Scriven counties, 
Georgia. In Washington County, Ga., good fire opal is 
obtained. Vhe Suanna Spring in Georgia affords small 
quantities of siliceous sinter. Tripolite occurs in Maine, 
New Hampshire, Nevada, California, and elsewhere. 
Tridymite. Pure silica, like quartz and opal, with very. nearly the 
hardness and specific gravity of opai, but occurring in tabular hexag- 
onal prisms, which are twins under the triclinic system. If not crys- 
tallized opal, it is a third state of SiO,. It occurs in trachytic and ~ 
some other volcanic rocks. Asmanite is from a meteorite, and may be 
the same as tridvmite. 
Jeneschite. Silica, $i0,, in, it is supposed. a fourth state, it resem- 
bling opal in aspect ‘and in solubility j in alkaline solutions, but having 
the specific gravity of quartz, or 26. From Hiittenberg in Carinthia, 
ote a white cachalong; from near Weissig ; Regensberg ; and 
in Brazi? 
Melanophlogite. Colorless cubes consisting of silica, with a little 
sulphuric trioxide and water. On sulphur from Girgenti, Sicily. 
