Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/442

Rh 424 MINERALOGY massive-granular) ; Rathlin and Magee Island, Ireland ; Faroes, Vesuvius (fig. 581), Sicily, Bohemia, Tyrol, -7 Nova Scotia. / **_/ e y Faroelite is a variety with 42 5 of silica. It replaces thomsonite generally in Tertiary igneous rocks, occurring at Storr and else where in the Hebrides, Faroes, Iceland, and Nova Scotia. The angle of the vertical prism is within 8 of that of thomsonite. It contains an equivalent more silica. 627. PREHNITE, A-lS i + 2CaSi + & . Right prismatic. ooP (m) 99 58 ; OP (c); 3Poo (e) 33 26 ; fPoo (v) 90 32 ; oof oo Fi S&quot; 582 ( S P- 626 )- (a); oopoo (b); P (s). Crystals either tabular of c, or prismatic along both the vertical and the brachydiagonal axes, hence varying much in form. Also in fan-shaped and botryoidal aggregations. Cl. c, perfect ; pearly thereon, vitreous else where. H. = 6 to 7; G. = 2-8 to 3. Transparent to translucent. Colour Fig. 583. Fig. 584. less, but generally green of bright but pale tints, also lemon-yellow. Becomes electrically polar by heat. B. B. intumesces greatly, melting to a porous enamel. Decomposed by h. acid. C.c.: silica 43 6, alumina 24 9, lime 271, water 4 4. Glen Gairn, Aber deen (fig. 583) ; Skye and Mull ; Corstorphine Hill (green and pink), Castle Rock (white), and Salisbury Crags (yellow), Edin burgh ; Frisky Hall, Dumbartonshire (fig. 584) ; Hartfield Moss, Renfrew (botryoidal); Cornwall; Dauphine; Tyrol: Cape of Good Hope; China ( Yu}. 628. FKIEDELITE, Mn 4 Si 3 Rhombohedral ; R 123 42 . OR ; ooR. Tabular habit, and in granular aggregates. Cl. basal, perfect. H. =4 to 5; G. = 31. Rose- red, with paler streak. C. c. : silica 36, protoxide of manganese 53, lime 2 96, water 7 9. Adervielle on the Neste do Louron (Pyrenees). HYDROUS SILICATES OF ALUMINA. These are probably for the most part products of decomposition of felspars under atmospheric exposure. 629. KAOLIN (Porcelain Earth], A- lS i 2 + 2H. Massive ; in beds and veins. Fracture uneven ; fine earthy, very soft, sectile, and friable. H. = 1 ; G. = 2 2. Opaque, dull. White or grey, inclining to blue, green, yellow, or red. Feels meagre, not greasy when dry, and plastic when wet. B.B. infusible. Not affected by h. acid, but decomposed by warm s. acid, leaving silica. C.c. very variable, but approximates to 46 silica, 40 alumina, and 14 water. Chiefly a product of the decomposition of orthoclase, or of granite, porphyry, and other rocks containing that mineral. Cornwall and Devonshire in England are the chief European locali ties for the kaolin used in manufacturing porcelain. Clays are merely varieties of kaolin, mixed with quartz-sand, car bonate of lime, magnesia, and the oxyhydrates of iron. Often 40 to 50 silica, 30 alumina, 13 to 20 water, and 4 iron peroxide, with lime and potash. In the fire the) are infusible, burning hard. Generally they are compact and friable, of white, yellow, red, blue, grey, or brown colours. Their specific gravity varies from 1 8 to 27. The following are varieties. Pipe-clay, greyish or yellowish white, with a greasy feel, adheres strongly to the tongue, when wet is very plastic and tenacious, and in the fire burns white. Abundant in Devonshire, and in the Trough of Poole in Dorsetshire; in France, Belgium, and Germany. Used for manufacturing tobacco-pipes and similar articles. Potter s Clay, red, yellow, green, or blue, becoming yellow or red when burnt ; more easily fused than the former, and often effervesces with acids. That used in the potteries in England comes chiefly from Devonshire. Loam, coarser and more impure, with more sand, and consequently less plastic. Shale or Slate Clay, greyish black, and much mixed with bituminous or carbonaceous matter. Bituminous Shale, known by its shining resinous streak. Black Clutlk, with more carbon, leaves a black mark on paper. Iron Clay contains much peroxide of iron, is reddish-brown, and forms the basis of many amygdaloids and porphyries. 630. NACRITE, AlSi 2 Right prismatic; minute six-sided tables in fan-like group ; and scaly. H. = -5 to 1 ; G. - 2 35 to 2 6. Glimmering to pearly, snow- white or yellowish white. C.c.: silica 46 3, alumina 39 - 8, water 13 &quot;9. A crystalline form of kaolin. Fins in Allier, Mons, Freiberg, Pennsylvania, and coal formation commonly. 631. LlTHOMARGE. Kaolinic substances, compact, earthy, and pseudomorphous. H. -2 5 to 3; G. -2 -4 to 2 6. White, yellow, or red. Greasy, adheres to tongue. Klausthal, Harz, &c. Similar are Carnat, Myclin, Melopsite. 632. HALLOYSITE, AlSi + 4H. Massive and reniform. H. = 1 5 to 2 5; G. 1 9 to 21. Trans lucent when moist. Bluish white, green, or yellow. C.c. : 41 5 silica, 34 4 alumina, 241 water. Hospital Quarry near Elgin, on the Tweed, Liege, Tarnowitz, Eifel (Lenzinite). Fuller s Earth may be an impure ferruginous variety. Maxton in Scotland, Reigate and Maidstone in England, Saxony, Bohemia, &c. 633. GLAGERITE, Al a Si 3 + 6H. H. - 1 ; G. = 2 &quot;35. Bergnersreuth. Malthazite, from Steindbrfel near Bautzen, has less alumina. 634. KOLLYRITE, Al a Si + 9H-. H. =1 to 2; G. =2. Also similar. Schemnitz, Pyrenees, and Saxony. Scarbroite from Scarborough has 10H 2 0. 635. MILOSCHIN. Conchoidal or earthy. H. =2; G. 21. Indigo-blue to celadon- green ; has 2 to 4 chrome oxide. Rudnik in Servia. 636. MONTMORILLONITE, Al 2 Si 7 + 2H. Massive. Rose-red. Montmorillon and elsewhere in France, Poduruoj in Transylvania. 637. RAZOUMOFFSKIN, AlSi 3 + 3H. From Carinthia. Chrome Ochre, with 2 to 10 per cent, of chrome oxide, from Waldenburg in Silesia and Creusot in France, is similar. 638. CIMOLITE, Al 2 Si 9 + 6H. Pseudomorphous after augite. Bilin, Limburg, Kaiserstuhl, Argentiera and Milo. 639. ALLOPHANE, AlSi + 5H. Botryoidal and reniform. Fracture conehoidal ; brittle. H. = 3 ; G. = 1 &quot;8 to 2. Pellucid ; vitreous. Pale blue, white, green, or brown. Colour due to copper. Charlton, Woolwich, Baden, and Bonn. 640. PYROFHYLLITE, AlSi^-t-H. Right prismatic, but radiated, foliated. Cl. perfect ; flexible, sectile. H. =1; G. =2 8 to2 - 9. Translucent, pearly. Light verdi gris-green to yellowish white. B. B. swells up with many twistings to a white infusible mass. C.c.: 67 silica, 28 alumina, and 5 water. Urals, Spa, Morbihan, Westana in Sweden, Carolina, and Brazil. Talcosite, from Heathcote in Victoria, has silica and alumina about equal. 641. ANAUXITE, AlSi 4 + 3H. Granular. H. =2 to 3 ; G. =2 2 to 2 &quot;4. Translucent, pearly. Greenish white. C.c.: 60 - 5 silica, 26 alumina, and 13 - 5 water. Bilin in Bohemia. HYDROUS SILICATES OF ZIRCONIA, THORJA, &c. 642. MALACONE, 3ZrSi + H. Pyramidal. P 83 30. Typical form ooPoo, P, o&amp;gt;P. H. -6; G. = 3 9 to 41. Conchoidal fracture. Lustre vitreous. C.c. same as zircon, but with 3 of water in the Hittero variety and over 9 in that from Finland. Has a surface opalescence, and may be altered zircon. Hittero, Chanteloube (near Limoges), near Dresden, Rosen- dal, Finland, Miask. 643. EUCRASITE. Right prismatic (?). II. =4 5 to 5; G. =4 39. Lustre greasy. Blackish brown ; streak brown. Translucent on edges. Fracture uneven; brittle. C.c. very complex : silica 16, thoria 36, cerium protoxide 5 5, peroxide 6, lanthania 2 4, yttria 4 3, erbia 1 6, titanic acid 1 3, ferric oxide 4 25, alumina 1 8, water 9. Barkevig near Brcvig. 644. THORITE, ThSi + 2H-. Pyramidal. ooP : P 133 30. Generally massive. H. = 4 5 to 5. G. 5 to 5 4. Lustre brilliant vitreous; when weathered resinous. Fracture conehoidal when fresh, splintery when weathered. Brownish black to clove-brown. C.c. complex, but essentially 18 silica, 73 thoria, 9 water. In syenite at Lochan