cinth-brown varieties are chiefly brought from Ceylon, and the smoky green and blue from Brazil, on which account they are often called Brazilian Emeralds and Sapphires.

Though the Tourmaline is occasionally used as a gem, it is chiefly interesting on account of its mineralogical characters, and certain curious physical properties which it possesses. The crystals are generally differently terminated, which is an exception to the law of crystallography, that all facets of the same kind should be similarly reproduced on all identically similar elements of a crystal. The electric properties of Tourmaline have relation to this crystallographical anomaly; and a prism heated in a particular way speedily manifests two kinds of electricity, becoming positively electrical at one end and negatively at the other. It becomes positively electrical when rubbed, and on being heated it becomes electrical while cooling, being positively electrical at the end of the crystal which has the greatest number of facets, and negatively at the opposite end. This state of polarity may be reversed by intense cold; and if a prism be broken while in an electric state by heat, the fragments present opposite poles, like artificial magnets. The crystals are also frequently particoloured, being of one colour at one end, and of another colour at the end opposite.

Cut in thin slices, and mounted in an instrument called a polariscope, the Tourmaline is used to analyse the optical properties of other minerals.

It is usually found in granite, gneiss, or mica-slate, also in Dolomite or granular limestone, and in sandstone near dykes of igneous rocks.

Black Tourmaline, or Schorl, is very abundant in almost all stanniferous granites, especially in Cornwall, in the neighbourhood of St. Austell, and in Devonshire, in the granite of Dartmoor, particularly near Bovey-Tracey. It also occurs in mica-schist at Karosulik, in Greenland; at Hörlberg, near Bodenmais, in Bavaria; at Käringbricka, in Sweden; with Emery, at Naxos; and in the U. S., at Haddam, Connecticut; Tasmania, imbedded in gravel, overlying granite, on Flinder's Island, in Bass Strait. The rare white variety is found on St. Gotthard, Siberia, and in Elba, in grey granite; the green variety (coloured by iron) near Katherinburg, in Siberia; Campo-longo, St. Gotthard, Canton of Tessin, and at Airolo, in Switzerland. Pale brownish crystals at Windisch Kappell, in Carinthia; also in Brazil, and elsewhere.

TREMOLITE.

TOWANITE. The name given by Brooke & Miller to Chalcopyrite, after the Cornish locality (Huel Towan), where fine crystals have been found.

TRAPEZOIDAL KOUPHONE SPAR, Mohs. See LEUCITE.

TRAPPISCHES-EISENERZ, Breithaupt. See

TITANIFEROUS IRON-SAND.

TRAUBENBLEI, Hausmann. See PYROMORPHITE.

66

TRAVERTINE. The name given to the harder and more compact kinds of Calcareous Tufa, formed by the evaporation of water holding lime in solution on the sides of rivers, waterfalls, &c. Large deposits of this nature are formed by some of the rivers and springs in Italy. The calcareous waters of the Anio incrust the reeds which grow on its banks, and the foam of the cataract of Tivoli forms beautiful pendant stalactites. On the sides of the deep chasm into which the cascade throws itself, there is seen an extraordinary accumulation of horizontal beds of Tufa and Travertine, from four to five hundred feet in thickness."Lyell's Principles of Geology, p. 241.

The name Travertine is derived from that of the River Tiber, and means Tiber-stone. Brit. Mus., Case 46.

M. P. G. Table-case B, in Recess 6, Nos. 206 to 210, and 219 to 223. TREMENHEERITE, Piddington. An impure Indian variety of Graphite. Analysis, from New Jersey: Carbon

Peroxide of iron
Earthy matter

Water and insoluble matter

85-7

100.0

Name. After Major-General Tremenheere, of the Bengal Engineers.

TREMOLITE, Jameson; TREMOLITH, Werner; TREMOLITHE, Brochant. A variety of Hornblende, differing from Actinolite principally in its pale green, grey, or white colour. It occurs both crystallized and in masses which have a columnar composition, and low degrees of transparency. The crystals are often in long slender blades, either distinct and traversing the gangues, or in columnar and radiated aggregations. The clear crystals are called Glassy Actinolite· the fibrous or thin capillary crystals Asbestiform Tremolite. The fibres are generally slightly elastic. S.G. 2.93.

Comp. Silicate of Magnesia and Lime.
Analysis, from Fahlun, by Bonsdorff:
Silica
Magnesia

60.10

24.31

Name. From Trinacria, an ancient name for Sicily.

TRIPEL, Werner. See TRIPOLI. TRIPE STONE. The name given to Anhydrite when composed of contorted plates,

which bear a sort of resemblance to the convolutions of the intestines. It is found

TRIPLITE, Dana, Hausmann, Nicol. RhomOccurs in compact crystalline masses, with bic primary form a rectangular prism. a lamellar structure and a cleavage in three directions perpendicular to each other. Colour from pitch-black to clove-brown. Opaque. Semi-transparent in thin fragments. Lustre resinous, adamantine. Streak Fracture flat-conchoidal. yellowish-grey. H. 5 to 5.5. S.G. 3.43 to 3.8.

Comp. Phosphate of protoxides of man

v. Kobell.

MENE. Derived

TRIPHANE, Brochant, (from Telavns, apHaüy. pearing three-fold. TRIPHYLINE, Dana, Fuchs, Nicol. Rhombic. Basal cleavage perfect. Commonly occurs in coarsely granular, crystalline masses. Colour greenish-grey; bluish in places, becoming brown and opaque when weathered. Slightly translucent, with a strong waxy lustre. Streak greyish-white. H. 5. S.G. 3.6.

SONITE.

See THOM

A

It

TRIPOLI, Jameson, Kirwan, Phillips. variety of earthy silica, or a fine arenaceous variety of Quartz mixed with clay. occurs massive with a coarse, dull, earthy fracture, is meagre and rough to the touch, and yields to the nail. Colour various shades of grey, yellow and red. Opaque. Soft and friable. S.G. 1.86 to 2.2.

It is found in veins in Tripoli, in Africa, (whence it was first brought and derived its name); at Arnberg, in Bohemia, near Prague; in Saxony, Thuringia, Tuscany, the Puy de Dôme in France, and near a stream seven leagues from Menat in Auvergne; Corfu, &c. Near Bakewell in Derbyshire, in upper Mountain Limestone.

Tripoli is used, when reduced to powder, for polishing metals, marbles, the glasses of optical instruments, and other hard substances. The Tripoli of Polinier, near Pontpean, four leagues from Rennes, in Brittany, is the most suited for lapidaries who polish gems of the first order. That approximating in colour to a yellowish-white should be preferred, because it is rarely sandy.

The Tripoli of Menat is produced from shale, by the spontaneous combustion of lignites.

TRIPPEL. See TRIPOLI.

TRITOMITE, Dana, Weibye & Berlin. A hydrous mineral related both in form and composition to Helvine and Garnet. Cubical. Tetrahedral. Cleavage indistinct. Colour dull brown. Subtranslucent. Lustre submetallic, vitreous. Streak dirty yellowishgrey.

Comp. R Si+2Ṁ. Analysis, by Berlin: Silica

Alumina

BB yields water and affords a weak fluorine reaction: with borax a glass which is reddish-yellow when hot, but becomes colourless when cold.

In powder, gelatinises in muriatic acid, with evolution of chlorine.

Locality. The Island Lamö, near Brevig, in Norway, in coarse syenite.

TROMBOLITE, Breithaupt. See THROм

2.24 40.36

Peroxide of lanthanium

Yttria.

0.46

5.15

Lime

TSCHERMIGIT, Kenngott. A kind of Ammonia-Alum.

It occurs compact and lamellar. Colourless or greyish-white. Lustre vitreous. Transparent to semitransparent. Brittle.

Streak white. H. 2 to 2.5. S.G. 1.75.

Comp. Am Al + 4HS or Am S+Al S+ 24H-ammonia 5·7, alumina 11.4, sulphuric acid 35-3, water 47.6=100·0.

Localities. Tschermig, in Bohemia, in the Brown Coal formation. The crater of Etna.

TSCHEWKINITE, Nicol, G. Rose. Massive or amorphous. Colour velvet-black. Nearly opaque. Lustre vitreous. Streak dark brown. H. 55. S.G. 4.5 to 4:56. Analysis, by H. Rose: Silica

. 21.04 20.17

3.50

0.22

0.83

11-21

BB becomes light blue and brittle: with soda fuses to an opaque mass.

New Red Sandstone.
Locality. The banks of the Tweed, in

Name. From Tuesa, the Latin name for the River Tweed.

Tuesite makes excellent slate-pencils.

TUFA. See CALCAREOUS TUFA; also TRAVERTINE, OSTEOCOLLA.

TUNGSTATE OF COPPER is said by Dr. Genth to occur in large crystals at Cosby's mine, Cabarras co., N. Carolina.

TUNGSTATE OF IRON, Phillips. See WOL

TURNERITE, Levy, Dana. A mineral containing alumina, lime, magnesia and a little iron. Colour yellow or brown. Transparent

TURQUOIS.

Fig. 443.

Locality. France, at Mount Sorel, in Dauphiny.

Name. Named by Levy after Mr. Turner,

in whose collection it was first noticed.

TURQUOIS, Dana, or TURQUOISE. There are two varieties of Turquois, the Oriental or Mineral Turquois (Turquois de vieille roche), and the Occidental or Bone-Turquois (Odontolite: Turquois de nouvelle roche).

The first, or true Turquois, occurs reniform, stalactitic or incrusting. Colour a peculiar bluish-green. Feebly translucent to opaque. Lustre somewhat waxy, internally dull. Streak white. Cleavage none. Fracture smail-conchoidal. H. 6. S.G. 2.6 to 2.83.

Comp. Diphosphate of alumina, or A12 Ï+5H (coloured by oxide of copper)= alumina 46.9, phosphoric acid 32-6, water 20.5=100.

Analysis of blue Oriental Turquois, by Hermann:

be bone or ivory coloured by phosphate of iron. It is of a sky-blue colour, passing into' greenish-blue and apple-green; frequently with black dendritical markings, which greatly impair its beauty and value. Its texture, which is very compact and earthy, exhibits traces of animal structure, in slender fibres of a lighter tinge than the rest of the mass, either parallel with or crossing each other, so as to present a sort of net-work, according as the section has been made parallel with or at right angles to the tusk.

The distinction is made in commerce between Turquois and Odontolite; the terms oriental and occidental being employed by inferior stones, than to denote any differjewellers rather to distinguish the finer from country. (Mawe.) ence either of chemical composition, or of

In the "Oriental accounts of the Precious Minerals," by Prinsep, it is stated, that "the Abu-Is'haqi (father of Isaac), or genuine turquois, is the produce of the mines of Ansar, near Nishapúr, in Khorasan (the same place mentioned as Michebourg, in Tavernier's Travels in India). All authorities concur that these are the only turquois mines in the world: the stones are said to vary from pale blue to green and white, but all except the azure are worthless. A curious fact is mentioned, also, which, from the nature of the mineral may readily be believed, though it has not been observed in Europe: the real blue turquois of Nishapúr changes in colour when kept near musk or camphor, also from the dampness of the ground, as well as from exposure to the fire (Pliny also remarks of the Callais quæ sunt earum pulchriores, oleo, unguento, et mero colorem deperdunt'); the inferior stones become discoloured even without this test by gradual decomposition or efflorescence.' *The Khawas-ul-hejar makes the clearness or dulness of the Turquois vary according to the atmospheric changes. 'It brightens the eyes; is a remedy for ophthalmia, and bites of venomous animals; it is used in enamelling sword handles,' &c. "The Badakshani Turquois essentially differs from the Nishapuri, in being able to withstand the heat of a fire for ten days

*When the Oriental Turquois becomes discoloured, it is only necessary to pass it over the mill, so as to remove the external surface, to restore its former appearance and colour. Odontolite when discoloured by time may be revived by immersion in a solution of oxide of copper, but the effect only lasts for a few days.