400 



THE POPULAR EDUCATOR. 



Borax, or lineal, crystallises in the monoclinic system in 

 short columnar crystals. It is a hydrated borate of soda. 

 Borax was originally brought from the shores of a salt lake in 

 Thibet ; the crude salt was termed tincal, and was purified 

 when it reached this country. Other countries now produce it, 

 especially certain lagoons in Tuscany. It is used as a flux in 

 metallurgical operations, and in the manufacture of imitation 

 gems. 



Boracitc is borate of magnesia. It crystallises in the first 

 system, and is found, with gypsum and common salt, near 

 Luneberg, in Lower Saxony, and other German localities. 



TUNGSTATES, TANTALATES, TITANATES, ETC. 



Wolfram is a tungstate of iron and manganese. It is trimetric, 

 occurring in modified rectangular prisms ; sometimes it is mas- 

 sive. It is dark-coloured, and usually found with tin ores. 



Sclieelite is a tungstate of lime. 



Tantalate, or columbite, is often confounded with tinstone, 

 which it closely resembles in appearance. It is a compound of 

 tantalic acid with iron and manganese, and occurs in rocks 

 containing albite and oligoclase. 



Sphene, or Titanite, is a silico-titanate of lime. It is 

 monoclinic, occurring in very oblique rhombic prisms. It has 

 a greyish-brown colour, and is found disseminated in separate 

 crystals through granite, gneiss, and other metamorphic rocks. 

 The crystals, from their wedge shape, give the mineral its name 

 (<70}i>, a wedge). The darker variety was termed titanite. 

 Titanic acid occurs in Brookite, rutile, and anatase. 



Having finished those minerals in which oxygen occurs, we 

 pass on to those which are devoid of that element. 



THE SULPHUKETS. 



The compounds of sulphur with the various metals are what 

 may be called the primary ores, all other ores being derived by 

 decomposition and oxidisation from them. It is supposed that 

 the combination of these elements was determined either when 

 the earth was in a molten state, or that it took place far down 

 in the earth's crust, and that by the internal heat the ore was 

 sublimed into the cracks of the rocks forming the crust, where 

 it to-day appears as lodes and veins. 



Realgar, or Red Orpiment, is the sulphuret of arsenic, and 

 is composed of 2 atoms of sulphur and 1 of arsenic. Its 

 crystals are oblique prisms of a splendid red, and having a 

 resinous lustre. 



Orpiment contains 3 atoms of sulphur. It is trimetric. Its 

 crystals are a beautiful yellow, and possess a pearly lustre. 

 Both these minerals have been used as paints. 



Grey Antimony, or Stibnite, is the sulphuret of that metal, 

 and is its chief ore. It is found massive, but when crystallised 

 it appears in trimetric prisms. Its colour is a lead grey. This 

 ore ' occurs in veins with silver, lead, zinc, or iron, or it is 

 associated with heavy spar or quartz. It was used by the 

 Greek ladies to blacken their eyebrows. 



Silver Glance (sulphuret of silver) crystallises in dodeca- 

 hedrons of the first system. It possesses metallic lustre, 

 and is a most valuable ore. It is found in Saxony, Norway, 

 Mexico, and Peru. 



Brittle Silver Ore is a sulphuret of silver and antimony. 

 It is trimetric, possesses metallic lustre, but, being an iron 

 black, is readily distinguished from silver glance. 



Ruby Silver is a variety of the above ore when the colour 

 approaches a cochineal red. In Mexico it is not uncommon. 



Light-red Silver has a similar composition to ruby silver, 

 but arsenic takes the place of the antimony. As the name 

 implies, the colour is not so dark. 



Galena, the sulphuret of lead, is monometric, possessing a 

 very perfect cleavage in planes parallel to the faces of the cube. 

 Its lustre is highly metallic, and a lead-grey. It is the chief 

 ore of lead, and is usually found with heavy spar for its matrix. 

 When the galena contains silver it is granular and less lustrous. 



Blende, or sulphuret of zinc, is monometric, with a perfect 

 dodecahedral cleavage ; it is also found massive. It has a 

 resinous lustre, and varies in its colour from yellow-brown to 

 black. It is found in lodes, -frequently with galena, and some- 

 times in positions which prove that it must have been deposited 

 from water. The miners call it Black Jack, as we have seen. 

 White Vitriol, Zinc Spar, and Calamine owe their existence to 

 the decomposition of blende. 



Cinnabar, the sulphuret oj mercury, is the source of the 



metal. It is rhombohedral when crystallised. Its colour ia 

 bright red, sometimes verging to grey. Its general situation ia 

 in slate rocks, but at Idria it is found in limestone. Almaden, 

 in Spain, is the only other European locality which yields it. 



Copper Pyrites, or yellow copper ore, is cur principal source 

 of the metal. Cornwall is its great repository, where upwards 

 of 150,000 tons are annually raised. It generally crystallises aa 

 an octahedron with a square base, or in the hemihedral form 

 a tetrahedron. Its colour is brass-yellow. It may be scratched 

 with a knife, which distinguishes it from iron pyrites. Its 

 composition is 4 atoms of sulphur, combined with 2 of copper, 

 and 2 of iron. By its decomposition many minerals are pro- 

 duced Hue vitriol, malachite, chrysocolla (hydrated silicate of 

 copper), black copper ore, and limonite (hydrated oxide of iron). . 



Grey Copper Ore, whenever crystallised, so invariably appears 

 in tstrahedra that it has been called tetrahedrite. No ore has 

 such a variable composition as grey copper ore. When it con- 

 tains 30 per cent, of silver in place of part of the copper, it ia 

 called o.rgentiferous grey copper ore or silver fahlery. It is 

 known in Germany to contain mercury, and when from 7 to 

 16 per cent, of this metal is present it is called spaniolite. The 

 grey copper ore of the Cornish mines is seldom argentiferous. 



Iron Pyrites is sulphuret of iron, and contains 2 atoms of 

 sulphur in combination with 1 of the metal. When 1 atom 

 of sulphur is combined with 1 of iron, magnetic pyrites is the 

 result a mineral which is slightly attracted by the magnet. 

 When found in crystals, which is seldom, they belong to the 

 hexagonal system. It is softer than ordinary pyrites. 



Pyrites is found when crystallised in cubes, or in pentagonal 

 dodecahedrons ; but it occurs massive, and in radiated lumps. 

 Its colour is bronze-yellow, is very hard, and strikes fire with 

 steel ; hence its name, from irvptTTjc,. It is found in rocks of 

 all ages, and is used to procure sulphur, sulphate of iron, 

 sulphuric acid, and alum. Good iron cannot be got from it on 

 account of the difficulty of entirely separating the sulphur. 



Erubescite, or horse-jlesh copper ore, is a double sulphuret 

 of copper and iron, containing 3 atoms of sulphur, 4 of copper, 

 and 1 of iron. Its colour is a dark flesh-red, hence its name j 

 but this it soon loses, and becomes iridescent, exhibiting a very 

 variegated appearance. 



Copper Nickel contains 1 atom, of arsenic and 2 of nickel. 

 It is copper-coloured, hence its name. It is frequently found 

 with cobalt, silver, and copper ores, and is the chief sourco 

 of nickel. 



Nickel Glance, or white nickel, is another arseniuret of 

 nickel, but it contains sulphur. Its colour is tin-white, and 

 it crystallises in cubes. Nickel is used to whiten brass, pro- 

 ducing German silver. 



Smaltine, or grey cobalt, is also monometric. It is usually 

 massive, having a granular and uneven fracture, and a tin-whito 

 colour. It is an arseniuret of cobalt. Any ore of cobalt is 

 readily recognised by the blue it imparts to a borax bead in the 

 blow-pipe flame. 



Cobaltine and cobalt pyrites are other ores of cobalt. 



Mispickel is arsenical iron pyrites. It resembles arsenical 

 cobalt, but is much harder. It occurs in trimetric rhombic, 

 prisms. It is frequently found in veins and in many crystalline 

 schists and serpentines. 



THE FLUORIDES AND CHLORIDES. 



Fluorine and chlorine are members of the group termed 

 halogens, because they combine directly with metals forming 

 salts. (See Hart's "Elementary Chemistry," Chap. XIII.) The 

 minerals thus formed are not numerous. 



Fluor Spar is fluoride of lime. It is the Blue John of the 

 Derbyshire miners, and is also termed Derbyshire spar. It 

 crystallises in cubes, and is usually of a violet colour. It is 

 frequently found in metallic lodes, particularly with galena and 

 barytes. It is found in the dolomite of Saint Gothard ; a rose- 

 coloured specimen is shown at the top of the Pass, for which 

 the collector asks 2,000 francs ! 



Cryolite is a double fluoride of sodium and aluminium. It 

 is semi-transparent and light- coloured, and has been called "ice 

 stone," because it melts in the flame of a candle. It was first 

 found in West Greenland. 



Rock Salt is the chloride oi sodium. It crystallises in cubes 

 of the first system. Its origin will be found discussed in the 

 chapter on the Triassic period in " Lessons in Geology." 



