Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/400

382 MINERALOGY Fig. 264. Almost always contains nickel, with cobalt, copper, and several minerals which are non-terrestrial. When polished and etched with nitric acid the surface is marked by lines of unaffected inter lacing crystals called Widmannstatten s figures ; most of the nickel is contained in these. Occurs in masses which vary in size from the smallest microscopic dust as dredged from the depths of the ocean to upwards of 32, 000 Tb. Many of these masses have been seen to fall. Several (suspected, however, to be terrestrial) have been found imbedded in a basaltic rock near Disco Bay in Green land, one of which is 44,000 K> in weight. Several contain hydrogen in their pores, condensed to the extent of eight times the volume of the mass; and the pitted depressions frequently observable upon their surface give countenance to the view that, if not dis charged from a volcanic throat, they were set at liberty by some sudden disrupting gaseous explosion. 17. ZINC, Zn . Rhombohedral. Said to be found in large hexagonal pyramids. Cl. basal, perfect. H. =2 ; G. =7. Lustre metallic. Colour and streak bluish white. Found in a geode in basalt near Melbourne, Australia, coated with smithsonite, erythrine, and aragonite. Also in the gold sands of the Mittamitta river. 18. COPPER, Cu. Cubic (figs. 28, 30, 26, 33, 37, 264). Twins, on an octahedral face. Crystals generally distorted. Often filiform and arborescent, or in plates and lamina;. H. =2 5 to 3; G. =8 5 to 8 9. Lustre dull metallic. Colour and streak copper-red, with yellow or brown tarnish. B. B. easily fusible, colouring the outer flame green. Sol. in n. acid. Occurs in many rocks (generally igneous), and frequently asso ciated with zeolites. In the Faroes, Unst (Shetland), Cornwall, Chessy near Lyons, the Banat (Hungary), Siberia, China, Mexico, Brazil, Chili, and Australia. Masses of great size are found, much the largest being from the Ontanagon river, on the south of Lake Superior. One mass found in February 1857 was 45 feet in length, 22 feet in width, and 8 feet in thickness; its weight was 420 tons. Another was found in 1869, 65 feet in length, 32 in width, and from 4 to 7 feet in thickness ; this weighed upwards of 1000 tons, and had a value of 400,000 dollars. 19. LEAD, Pb. Cubic, but only in thin plates, capillary or filjform. Cl. none. H. =1-5; G. =11-36 to 11 4. Ductile, malleable, and sectile. Bluish grey, but with a blackish tarnish. Found in lava in Madeira, and at the mines near Cartagena in Spain ; in amygdaloid near Weissig ; in basaltic tufa at Rautenberg in Moravia ; with gold near Mount Alatau in the Altai, at Velika in Slavonia, and at Olahpian in Transylvania ; near Ekaterinburg in the Urals ; in the district of Zomclahuacan in Vera Cruz, in foliated galena, in granular lime stone ; in the iron and manganese bed of Paisberg in Wermland (Sweden), with haematite, magnetite, and hausmaunite ; in white quartz, north-west, near the Dog Lake of the Kaministiquia, an affluent of Lake Superior ; imbedded in hornstone in plates and grains, in the mine of Bogoslovskoi in the Kirghiz steppes; in green stone porphyry at Stiitzerbach in Thuringia ; with haematite in the islands of Nias on the west coast of Sumatra. 20. MERCURY, Hg. Cubic. Occurs in small liquid globules in its gangue, but may be solidified at - 39, when it forms octahedral crystals. G. = 13 596 when liquid, 15 612 when solid. Lustre brilliant metallic; tin- white. B. B. volatile, sometimes leaving a little silver. Readily sol. in n. acid. Occurs generally in clay shales or schists of dif ferent ages. The globules of mercury are usually found in rents in cinnabar, or accompanying calomel, at most of the localities for these minerals. Found at Idria in Carniolaand Almaden in Spain. At Idria it is obtained by washing a soft clay slate. In Transylvania and Galicia springs issuing from the Carpathian sandstone bear along globules of mercury. At the Pioneer mine in California some of the quartz geodes contain several pounds of mercury. At Cividale in Lombardy it is found in an Eocene marl. It has also been observed occasionally in drift, and has even been stated to have been found in a peat bog. 21. SILVER, Ag. Cubic (figs. 26, 30, 33, 40, 37). Crystals generally small, also and most frequently filiform, arborescent, and in plates or crusts. These either project into cavities, coat their surfaces, or ramify in a reticu lated manner throughout the mass of the rock. Twins of octahedral and trapezohedral composition. Noel. H. =2 5 to 3; G. =101 to 11 - 1. Lustre metallic. Colour and streak silver- white, but generally tarnished yellow, brown, or black. Malleable, ductile, and sectile, but less so than gold. B. B. easily fusible. Sol. in n. acid ; the solution colours the skin black. C.c : silver, with varying proportions of gold, platinum, mercury, copper, antimony, and bismuth. The auriferous from Norway contains silver 72, gold 28 ; from quartr reefs in Sutherland, silver 71 4, gold 28 (3. The cupriferous from Courcy near Caen contains 10 per cent, of copper. The antirnonial from Bohemia contains 1 per cent, of antimony. The mercurial from Kongsberg in Norway has - 4 of mercury, found chiefly in veins in gneiss, clay slate, and limestone. Localities : Alva and elsewhere in Scotland, Ballycorus in Ireland, and Cornwall in England ; at Freiberg, Andreasberg, and Kongsberg ; along with native copper at Lake Superior ; in Mexico, in Peru, and in the United States. The finest crystallized silver occurs at Lake Superior, and at Kongsberg. At the last locality the crystals are an inch in diameter, and are disposed on large filiform brushes. Silver occurs in large masses ; three of 436, 560, 812 lb have been recorded from Kongsberg. A block which smelted 44,000 lb was for some years used as a table by Duke Albert on his annual visits of inspection to the Schueeberg mine in Saxony. A Mexican specimen was found of 400 lb ; the mines of Huantaya in Peru have yielded masses of 444 and 960 R>. Britain produces annually about 760,000 oz. of silver, chiefly, however, from lead ores. The value of annual produce for the whole world from all sources is from 8 to 10 millions of pounds sterling. 22. SCHNEIDERITE (Gold Amalgam), Au 2 Hg 3 . Tetragonal four-sided prisms, easily crumbling, yellowish white to white ; sometimes in grains the size of a pea. C.c. : gold 41 63, mercury 58 37. Found at Mariposa in California. A variety (Au, Ag) 2 Hg s is found along with platinum in Columbia ; this contains gold 38 39, silver 5, mercury 57 40. 23. ARQUERITE, Ag 6 Hg . Cubic. In octahedra, also in grains and dendrites. G. =10 8. Like native silver, but softer. C. c. : silver 86 - 5, mercury 13 5. From Arqueros in Coquimbo, Chili. Kongslergite, Ag 18 Hg, occurs at Kongsberg, with 95 - 1 of silver and 4 9 of mercury. 24. AMALGAM, Ag.Hg 2 , andAgHg 3 . Cubic (fig. 33, in combination with 40, 30, 41, 38). Cl. dodeca- hedral. H. =3 to 3 "5 ; G. =10 "5 to 14. Colour and streak silver- white. Fracture conchoidal, brittle, grates when cut. In closed tube yields mercury and leaves silver. Sol. in n. acid. The first variety (silver 34 8, mercury 65 2) occurs at Moschellandsberg in the Palatinate, where the veins of mercury and silver intersect one another; the second (silver 26 25, mercury 7375) there, and also at Allemont in Dauphine, Almaden in Spain, in Hungary, and in Sweden. From Rosilla in Atacama (Chili) Domeyko reports the following other compounds : Ag 3 Hg 4 , silver 46 8, mercury 53 2, white and silvery ; AgHg, silver 55 1, mercury 44 9, granular and dull; Ag 5 Hg 3 , silver 64 2, mercury 35 8; of the last there is a mass weighing 22 lb in the museum of Santiago. 25. GOLD, An. Cubic (figs. 30, 26, 33, 40, 36) and more complex forms. Crystals generally small and indistinct through elongation, assuming capillary and arborescent shapes. Also in thin plates. Twins rare; twin face octahedral. Frequently in rounded and apparently colloidal masses impacted in clay, or loose in small grains (pipettes) rolling in the bed of streams. Fig. 265 is of such a mass found in Sutherland. No cl. H. =2 5 to 3 ; G. =17 to 19 "4. Lustre metallic, but fre quently dull and partly coated with a brown crust. Colour and streak yellow ish white to bright gold- yellow. Malleable, ductile, and sectile ; the purer varieties the more so and the softer. B. B. easily fusible. Sol. in aqua regia, generally with precipitation of chloride of silver. Solu tion yellow, stains skin purple-red, with corrosion. C.c. : gold, with silver from 72 to 26 per cent. ; sometimes iron and copper under 1 per cent. Found in beds and veins generally of quartz in metamorphic rocks of a schistose nature, rarely in diorite and porphyry, and very rarely in granite. Its general associate is limonite, formed from decomposition of pyrite ; sometimes also haematite and magnetite. Occurs also in microscopic grains in quartz, from which it is extracted by crushing and amalgamation. The geologic range is from the Azoic to the Tertiary and Cretaceous, as in California ; but even in these more recent rocks the original source must have been at least Palaeozoic. Of localities which yield gold the following may be noticed : the Leadhills in Scotland, Wicklow in Ireland, Dolgelly in North Wales, Cornwall in England ; Transylvania, Hungary, and Piedmont ; the Urals, Ekaterinburg, and India ; Kordofan, the coast opposite Madagas car, and the Gold Coast (the fame of which has been recently re vived) ; Minas Geraes in Brazil, Bolivia, North Carolina, and

Fig. 265.