Tolfa near Rome, where it occurs in small geodes in decomposed trachytic rocks, and owes its origin to the action of sulphuric acid (a product of volcanic agency) upon the rock during long periods of time (Muzay, Hungary; Montdore, Auvergne).

E. BORATES.

76. Boracite.-Monometric, tetrahedral. The crystals sometimes show combinations of the cube, the rhombic dodecahedron, and tetrahedron. Always porphyritically imbedded. Cleavage imperfect. Fracture conchoidal. Brittle. H.=7. S.G. 2.97. Colourless, white or greyish, yellowish, greenish. Lustre vitreous to adamantine. Transparent to translucent at edges only. Cp.-MgB4. Bp. intumesces, fuses with difficulty, forming a pearl which, whilst hot, is transparent and yellowish, and when cooled is white and crystalline, acicular. It colours the flame green when fused with sulphate of soda and fluor spar. In muriatic acid it is perfectly soluble. Boracite occurs, as an accessory only, in gypsum, anhydrite, or rock-salt (Lüneburg in Hanover, Seegeberg in Holstein, Luneville in France; in the last place in radiated fibrous masses). A fine-grained to compact rock, which occurs in subordinate masses in the salt mountains of Stassfurt near Magdeburg, consists essentially of boracite with some chloride of magnesium. It is called stassfurtite.

H.=

77. Borax (Tinkal).-Monoclinic, isomorphous with pyroxene. The crystals usually broad and short, columnar. Cleavage clinodiagonal and prismatic. Fracture conchoidal. 2-2.5. S.G.=1.72. S.G. 172. Colourless, or more usually yellowish and greyish-white. Lustre resinous. Translucent. Cp. == NaB2+10H; usually impure. Bp. decrepitates with rapid heating, puffs up violently, becomes black, and finally melts to a transparent colourless powder. It tinges the flame reddish

yellow. If moistened with sulphuric acid, it tinges the flame green.

Borax is met with in loose crystals and crystalline grains or incrustations, associated with rock-salt, on the shores of several lakes in Thibet, where it is a recent formation. Clear lake in California, in crystals several inches long.

F. PHOSPHATES.

(a) ANHYDROUS PHOSPHATES.

78. Apatite (Spargelstein, Phosphorite).-Hemihedral hexagonal. The crystals short, columnar, or tabular; also massive, in granular, fibrous, or compact masses (phosphorite). Cleavage prismatic and basic. Fracture conchoidal to uneven, and splintery. Brittle. H.-5. S.G.=3.25. Colourless, white, but more usually light green, blue, or grey. Lustre vitreous on crystal faces; resinous on fracture or cleavage surfaces. Cp.=3Ċa3Ï+Ca(Cl,F), with sometimes Mg and Fe. Bp. only fusible in thin lamina. If moistened with sulphuric acid, colours the flame bluish-green. Soluble in muriatic and in

nitric acids.

Apatite is met with—(1) as an independent rock or in concretions, principally in strata of the Browncoal formation, more rarely in the Chalk formations, always massive (phosphorite); frequent in the Oberpfalz of Bavaria: (2) as an accessory constituent of rocks, especially the volcanic (nepheline-dolerite at Löbau in Saxony; basalt in Bohemia; volcanic rocks of Tumilla and in meteorites); in talc-schist (Zillerthal), and in limestone (Gouverneur in North America, Arendal, Pargas); (3) very frequent in veins of tin-ore.

It will be therefore seen that apatite in many cases must be a formation by wet process, and in others a plutonic product. Daubrée has succeeded in producing artificial crystals of

apatite by conducting fumes of chloride of phosphorus over

heated quicklime.

79. Turquois (Calaite).-Amorphous in cavities and veins, reniform or stalactitic. Fracture conchoidal to uneven. H.=6. S.G. 2.6-2.8. Colour sky-blue to verdigris-green.

Streak

greenish-white. Lustre feeble. Translucent at the edges to opaque. Cp.=Ä11Ï+5H, with some Cu up to 3 per cent. If heated in test tube, it gives water, decrepitates violently, and becomes black. Bp. infusible; tinges the flame green. Soluble in acids.

Turquois is met with as an incrustation in the fissures of Lydian stone; very precious varieties in Persia. Also occurs

in sandstone in Arabia.

(b) HYDROUS PHOSPHATES.

80. Vivianite (Blue Iron-Earth).-Monoclinic. The crystals usually single, attached, also fibrous, divergent, earthy. Cleavage clinodiagonal, very perfect; in thin laminæ, flexible. H.= 1.5-2. S.G.=2.66. Colour indigo-blue to blackish-green, sometimes white, and becoming blue by exposure. Lustre on cleavage surfaces, mother-of-pearl. Translucent. Cp.-Fe3+ 8H. Bp. in matrass gives out much water, puffs up, and becomes particoloured grey and red; on charcoal burns and becomes red, and then fuses to grey, lustrous, and magnetic globule. Readily soluble in muriatic and nitric acids.

Vivianite is usually a product of decomposition from magnetic pyrites, in veins traversing the clay slate (St. Agnes, Cornwall), or in granite (Bodenmais in Bavaria). The earthy variety is very frequent as an accessory constituent of turf mosses and Tertiary clays. Pseudomorphous in form of oysters and belemnites in New Jersey, U. S.

81. Wavellite (Lasionite).-Trimetric. The crystals usually small, acicular, and clustered to reniform aggregates of radiated

structure. H.-3.25-4. S.G. 2.34. Colourless, white, or coloured greyish, or a beautiful green or blue. Lustre vitreous. Cp.=(Äl1Ï+18H)+AIF. Bp. in matrass gives out water and traces of hydrofluoric acid. In the forceps puffs up and tinges the flame bluish-green, especially if moistened with sulphuric acid.

Wavellite is met with as an accessory and a secondary product in fissures of a soft clay-slate at Barnstaple in Devonshire; in Lydian stone at Langenstriegis, near Freiberg; and in Devonian sandstone at Zbirow in Bohemia.

G. NITRATES.

82. Nitre (Saltpetre).—Trimetric. The crystals prismatic, isomorphous with aragonite, but usually only very thin, capillary, and acicular. Fracture conchoidal. H.=2. S.G.

19. Colourless, white and grey. Lustre vitreous. Taste saline, cooling. Cp.=KN. Readily soluble in water; deflagrates vividly on glowing charcoal. Bp. fuses easily on platinum wire, tinging the flame violet.

Nitre occurs as a separate formation in the caverns of several limestone mountains (Ceylon, Calabria), as an efflorescence from the surface of the ground, especially in hot weather after rain (Aragon, Hungary, East India); also in springs.

83. Nitratine (Chili saltpetre).—Rhombohedric. In crystals, and crystalline grains; cleavage, rhombohedric. H.-1.5-2. S.G. 2.1-2.3. Colourless or light coloured. Transparent to translucent. Taste saline, cooling. Cp.-NaN. Soluble in water; deflagrates in glowing charcoal, but less vividly than saltpetre. Bp. fuses, tinging the flame yellow.

Nitratine is a marine product, found in grains mixed with the sand, and associated with gypsum, rock-salt, and glaubersalt, occurring at many parts of the coast of Chili.

H. CARBONATES.

(a) ANHYDROUS CARBONATES.

The most important of the carbonates are those comprised in the Calcite group. The calcspar and dolomites form whole mountain ranges (limestone and dolomite) as well as isolated mineral formations of minor extent in cliffs, fissures, and veins.

They are chiefly of neptunian origin, partly crystalline or compact precipitates; partly formed by springs; and partly the result of organic processes (chalk, coral). There are probably no limestone rocks of plutonic origin, although carbonate of lime under high pressure is capable of fusion without chemical decomposition. The minor mineral formations in clefts, veins, dykes, and geodes are doubtless, for the most part, the result of infiltration.

All calcites are rhombohedral in crystallisation. Calcspar alone presents great variety of form. Its crystals are grouped and interlaced in almost every conceivable shape and fashion, and the uncrystallised varieties are fibrous, granular, compact. The cleavage of the crystals is rhombohedral, very perfect. The angle of the cleavage rhombohedron is the most characteristic distinguishing feature of the different species, which can only be determined in many cases by an accurate measurement of that angle. Fracture conchoidal, but in the crystallised varieties it is somewhat difficult to obtain a genuine fracture. The colour is usually white, grey, yellowish, reddish, or brownish. Lustre vitreous, sometimes resinous. Calcspar and magnesite alone are sometimes perfectly transparent, the other calcites at most only attain translucence. The Cp. of all calcites comes under the general formulæ RC.

The following are the principal species of this important group of minerals :