Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/436

Rh 418 INERALOGY 579. ARFVEDSONITE, RSi + FeSi 3. Oblique prismatic. oP; o&amp;gt;P c oo ; P; 2P c oo 120 24 ; OP. Cl. oP 124 22, perfect; also OP. Massive. Black; opaque. Vitreous. H. =6; G. =3 44. C.c. : silica 43, alumina 4 5, peroxide of iron 3 8, protoxide 34, lime 57, soda 8 5. Streak dark blue-grey. Fusible in fine splinters in the flame of a candle. B.B. intu- mesces and melts easily to a black magnetic globule. Not sol. in acids. Kangerdluarsuk in Greenland, Frederiksvarn, Arendal, El Paso in Colorado. 580. PlLOLITE, Felted or matted fibres more or less dense. Cream yellow to buff. Dull ; extremely tough ; absorbs water like a sponge. H. = 1 to 2 5 ; G. = 68 to 1 34. Structure varies considerably, and has given rise to trivial names, as mountain paper, mountain leather, mountain flesh, rock cork, &c. Mountain Paper occurs in thin sheets at Boyne Castle near Banff ; Mountain Leather, Burn of the Cairn (Cabrach), Tod Head (Kincardineshire), Leadhills, Strontian ; Rock Cork, Portsoy and Boyne Castle, Saxony, and Sweden. C.c. : silica 51 6, alumina 8 6, ferrous oxide 2 88, magnesia 10 2, water 23 3. 581. KROKIDOLITE, 3FeS i + (Na, Mg)Si 2 + 2H-. Delicate, easily separable, but tough fibres ; elastic. H. = 4 ; G. = 3 &quot;2 to 3 3. Translucent ; silky. Indigo-blue ; streak lavender. B.B. fuses easily to a black magnetic glass. C.c.: silica 50 3, iron protoxide 35, magnesia 2 - 2, soda 67, water 5 8. Stavern in Norway, Greenland. A fibrous yellow mineral from Orange river, South Africa, has been referred here ; its fibres are not separable, and its hardness is 7. Abriachanite, a very similar mineral, of blue colour, occurs near Inverness. 582. GLAUCOPHANE, 9RSi + 2AlSi 3. .Oblique prismatic. Cl. prismatic, perfect; fracture conchoidal. H. = 5 5; G. =3 1. Translucent; vitreous to pearly. Indigo- blue, grey, bluish black. B. B. becomes brown, fusing easily to olire-green glass. C.c.: silica 56 5, alumina 12 2, protoxide of iron 10 9, magnesia 8, soda 9 &quot;3. Island of Syra. 583. HERMANNITE, MnSi. Granular and arborescent. Rose-red. G. =3 4. C.c. : protoxide of manganese 46 7, silica 48 9, lime 2, magnesia 2 4. Cummingtou in Massachusetts. 584. GRUNERITE, FeS i. Asbestiform. G. =37. Brown; silky lustre. C.c.: protoxide of iron 51 55, silica 45 - 45. Mt. des Maures (Var). 585. IOLITE (Cordierite, Dichroite), A 2 Si 3 + 2(Mg, Fe)Si. Right prismatic. ooP (P) 119 10, middle edge of P 95 36. Form ooP (T), oopoo (1), OP (m) ; and this with oopoo (k), ooP3 (d), Poo (n), and |P (s), (fig, 518); short, prismatic. Cl. coPoo distinct, traces along Poo ; fracture conchoidal or uneven. H. =7 to 7 5; G. =2 5 to 27. Trans parent or translucent ; vitreous, inclining to resinous. Colourless, but chiefly dark blue, or violet, green, brown, yellow, and grey. Often with distinct trichroism ; on OP blue, on ooPoo grey, and on ooPoo yel lowish. B.B. fuses difficultly to a clear glass; slightly affected by acids. C.c.: 48 to 51 silica, 29 to 33 alumina, 8 to 13 mag nesia, 1 to 12 iron protoxide. Cabo de Gata in Spain, Bodenmais (Peliom), Orijerfvi in Finland (Steinheilite), Norway, Sweden, Greenland, North America, and Siberia. Small rolled masses of an intense blue colour and transparent, found in Ceylon, are the Sapphire d Eau or Luchssapphir of the jewellers. The following have been considered cordierite altered, or with 2 to 6 atoms water : (a) Bonsdorfite, Hydrous lolite, greenish brown or dark olive-green ; near Abo. (b) Esmarkite, Chlorophyllite, large prisms or foliated, green or brownish ; near Cabrach (Aberdeen), Breyig in Norway, Unity in Maine, and Haddam in Connecticut, (c) Fahlunite, Triclasite, compact, greenish brown or black, foliated H. =2 5 to 3; G. =2 5 to 2 8 ; Falun, (d) Huronite, granular pearly, yellowish-green; H = 3 3; G. =2 86; infusible and insol uble ; Lake Huron, (e) Weissite, kidney-shaped and ash-grey or brown ; Falun and Lower Canada. (f) Pyrargillite, indistinct imbedded crystals, black passing into brown or red, dull resinou lustre; H. 3 5 ; G. =2 5; Helsingfors. (g) Finite, crystallized, or massive and laminar, with imperfect cleavage ; H. = 2 to 3 G. 27 to 2 9, semitranslucent or opaque, dull or resinous, am: dirty grey, green, or brown ; B. B. fuses to a glass, sometimes clear, at other times dark-coloured ; Auvergne, Schneeberg, Penig Saxony, the Harz, Cornwall, Cabrach and Torry (Aberdeenshire), 18. Geroldsau in Baden, snow-white, opaque, fragile, is similar, (h) Gigantolite ; H. =3 5 ; G. =2 8 to 2 9 ; opaque, dull resinous, and greenish grey or brown ; B. B. intumesces slightly, and fuses easily and green; Brevig in Norway. 586. EMERALD (Beryl], AlSi 3 + SGISi . Hexagonal ; P 59 53 . Crystals of ooP, OP, and ooP, ooP2, OP, P [a, p, c, s, fig. 519) are prismatic, generally with vertical striae. Cl. basal, rather perfect; ooP im perfect. H. = 7 5to8; G. =2 6 to 2 8. Transparent or trans lucent ; vitreous. Colourless or white, but generally green, some times very brilliant; also yellow and smalt-blue. B. B. melts with difficulty on the edges to an obscure vesicular glass. Not affected by acids. C.c. : 67 5 silica, 187 alumina, and 13 8 glucina. with 3 to 3 iron peroxide, and 3 to 3 5 chrome oxide in the rich green emerald. Emerald, bright green ; G. =2710 to 2759; occurs in Muso Valley near Bogota, also in Salzburg and the Urals. 519. or Aquamarine, colourless, or less brilliant; G. =2 677 to 2725 ; near Mursinsk and Nertchinsk in Siberia, Salzburg, and Brazil ; in the United States, where at Grafton, between the Connecticut and Merrimack, crystals 4 to 6 feet long, and weighing 2000 to 3000 lt&amp;gt;, occur ; Mourne Moun tains in Ireland ; Mount Battock and Cairngorm in Scotland (fig. 98). Common Beryl at Falun in Sweden, Fossum in Norway, Limoges in France, Rabenstein in Bavaria, Nigg Bay and Pitfodels and Rubislaw near Aberdeen (Davidsonite), Struay Bridge (Ross). Emerald and beryl are much valued as precious stones. Known from quartz by face p. Forms shown in figs. 92, 95, 96, 97, 98, 276. 587. LEUCOPHANE, 6CaSi + 3G1S1 + 2NaF. Right prismatic. ooP 91&quot;. Cl. basal perfect. H.=3 5 to 4; G. =2 97. Pellucid. Wine-yellow to olive-green. Vitreous. B.B. fuses to pale violet-blue bead. C.c. : silica 47, lime 23 &quot;4, glucina 107, soda 11 3, fluorine 6 6. Lamo in Norway. 588. MELINOPHANE, 7(R.)Si 2 ) + 6NaF . Pyramidal. P 122 23 . &quot;Mostly lamellar. II. =5; G. = 3, Honey-yellow to citron-yellow. Brevig and Frederiksvarn. FELSPAR GROUP. Crystallization oblique prismatic or anorthic ; very similar both in aspect and in angles. Cl. very distinct, especially the basal P; less so the clino- or brachydiagonal M. G. =2 4 to 3 2, but mostly 2 5 to 2 8 ; H. =6 or a little more. Slightly or not at all soluble in acids. B.B. fusible, but often with difficulty. Translucent; pure varieties transparent. Colourless, white, or shades of red ; less commonly of green or yellow. C.c. : anhydrous silicates of alumina, and of an alkali or alkaline earth. The felspars are very important constituents of the earth s crust, occurring in nearly all the igneous rocks, and in many of the stratified crystalline schists. In true strata they are found chiefly as fragments or decomposed, and in the latter state form a large part of wet soils and clays. By the older mineralogists and in popular language many species are conjoined under the common name of felspar which are now considered as distinct, each of them having not only its peculiar physical and chemical characters, but also geognostic position and associated groups of minerals. Thus ortlioclase, and the other more siliceous felspars with potash, abound in granite and the plutonic rocks ; the less siliceous, with soda and lime, characterize the volcanic rocks, e.g., labradorite the basaltic group, glassy felspar the trachytic. Orthoclase is associated with quartz, hornblende, and mica; glassy felspar either with hornblende and a black mica or with augite ; labradorite with augite, very rarely with quartz or hornblende. The felspars are best known from similar minerals by their hard ness (they scarce scratch with a good knife), difficult fusibility, and unequal cleavages. The following marks may aid the student in distinguishing the more common species. In orthoclase the basal cleavage plane forms a right angle with the cliuodiagonal cleavage planes M on both hands ; in the triclinic or plagioclase felspars- the angles are unequal. Orthoclase, albite, andesinc, and oligoclase are insoluble in acids ; labradorite and anorthite are more or less soluble. In granite, when decomposing, orthoclase often becomes reddish or dark-red ; oligoclase dull green, and at length white. Waltt riiauscn considers that the felspars are mixtures of throe true species, forming a series with the oxygen of the silica, alumina, and RO in the proportions x : 3 : 1, x ranging from 24 to 4. Tcher-
 * he United States, and Greenland (Gieseckitc, sp. 650). Oosite from
 * o a greenish slag ; Tammela in Finland. (i) Praseolitc, lamellar