Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/430

412 MINERALOGY SCAPOLITE GROUP. 499. SARCOLITE, 8Ca, 3A1, Na, 9Si . Pyramidal. P 102* 54 ; ooPoo ; OP; P, and other faces as in fig. 480, many of the faces being alternately hemihedral. H. =5 5 to 6 ; G. = 2 93. Vitreous. Grey to rose-red. Translucent; very brittle. C.c. : alumina 21 5, lime 32 4, soda 3 "3, silica 40 5. B.B. fuses to a white enamel; gelatinizes with acids. Somma. Fig. 480 (sp. 499). Fig. 481 (sp. 500). 500. MEIONITE, 6(Ca, Na), 4A1, 9Si. Pyramidal. P (o) 63 42 ; Poo (t); ooP (a); ooP (6) (fig. 481). Cl. macrodiagonal. H. -=5 5 to 6; G. = 2 6 to 274. Vitreous. Colourless or white. Transparent. Much cracked. C.c.: 31 9 alumina, 26 - 2 lime, 41 9 silica. Gelatinizes iu acids. Somma. 501. MIZZONITE, 6(Ca, Na), 4&1, 15Si. Pyramidal ; P 64* 4 (fig. 482). Similar to meionite. C.c.: alumina 23 8, lime 8 8, soda 9 8, silica 547. Insoluble in h. acid. Somma. 502. SCAPOLITE, 3(Ca, Na)Si + LJ3i, . Fi g- 482 ( S P- 501 )- Pyramidal. P 63* 42 ; ooPoo ; P ; ooP ; also massive. Cl. ooPoo, perfect; and ooP. H. -5 to 5 5; G. =2 6 to 2 8. Trans parent or translucent ; vitreous, pearly, or resinous. Colourless, but also pale grey, green, yellow, or red. B.B. melts with effervescence to a vesicular glass; in the closed tube may show traces of fluorine; with solution of cobalt becomes blue. Sol. in h. acid. C.c.: 49 silica, 28 alumina (with iron peroxide), and 23 lime (with soda). Tiree (Scotland), Arendal, Tunaberg, Pargas, Massachusetts, and New York. Known by its rectangular cleavage, resinous lustre on fractured surfaces, and action B.B. Dipyre, P 64 4 , is a variety. 503. MELLILITE (Humboldtilite), 2(Ca, Mg)Si 2 + (Al, Fe)Si . Pyramidal. P 65 30 ; OP; ooPoo. Cl. basal, perfect. H. =5 to 5 5; G. =2 91 to 2 95. Translucent on edges ; vitreous to resin ous. Honey-yellow, orange-brown, and yellowish white. C.c.: 32 lime, 7 magnesia, 9 alumina, 7 iron peroxide, 40 silica. Capo di Bove, and Vesuvius. 504. GEHLENITE, (Ca, Fe) 3 Si + (Al, Fe)Si . Pyramidal. P. 59* ; OP; ooPoo ; ooP3; 2P. Cl. basal. H. =5 5 to 6 ; G. =2 9 to 3 1. Translucent on edges. Dull resinous. Mountain-, leek-, or olive-green, and liver-brown. C.c.: 22 alumina, 5 iron peroxide, 35 lime, 4 magnesia, 31 4 silica. Mon- zoni in the Fassa Valley. NEPHELINE GROUP. 505. LEUCITE, Al, Si 3 + KS i . Pyramidal. Combination of the ditetragonal pyramid (i) with the tetragonal pyramid *?), and 2Poo (u) with ooP(m). Hemitropes united Fig. 483. Fig. 484. by (u}. Fracture conchoidal. H. = 5 5 to 6; G. 2 4 to 2 - 5. Trans parent to translucent on the edges; vitreous, inclining to resinous. Colourless, but greyish, yellowish, or reddish white ; streak white. B.B. infusible; with cobalt solution becomes blue. Sol. in h. common ; also fig. 485. acid, without gelatinizing. C.c.: 54 - 9 silica, 23 6 alumina, and 21 5 potash. Abundant in the lavas of Vesuvius, the tufas near Rome, and the peperino of Albano ; also at the Kaiserstuhl, and near Lake Laach. Readily distinguished from analcime by its in- fusibility, and by never showing faces of the cube. 506. NEPHELINE (Elaeolitc), AlSi + 4(Na, K)Si. Hexagonal. P 88 10 . ooP, OP, P Crystals imbedded, or in druses ; also massive-granular; fracture conchoidal, or uneven. H. =5 5 to 6; G. =2 58 to 2 64. Transparent or translucent ; vitreous and resinous. Colourless or white (nepheline) ; or opaque, dull resinous, and green, red, or brown (eheolite). B.B. melts difficultly (nepheline), or easily with slight effer vescence (elseolite), into a vesicular glass. Sol. and gelatinizes in h. acid. C.c. : 41 2 silica, 35 3 alumina, 17 soda, 6 "5 potash. Nepheline at Monte Somma, Capo di Bove, Katzenbuckel in the Odenwald, Aussig, and Lusatia. Elneolite in the zircon syenite at Laur- vig, Fredriksvarn, Brevig, and Miask. Fig. 485. Davine, with P 51 46 , seems only a variety; as also Cancri- nite, bright blue, and with some carbonate of lime. 507. MICROSOMMITE, RSi + AISi + NaCl . Hexagonal. a>P;OP; ooP2;ooP*. Cl. ooP. H.=6;G.=2 42 to 2 53. Colourless to yellow; lustre silky. Somma and Vesuvius. 508. SODALITE, 3(AlSi + NaSi) + NaCl. Cubic ; ooO, and fig. 486 ; generally distorted ; also massive and granular. Cl. o0 ; fracture conchoidal or uneven. H. = 5 5 ; G. = 2 1 3 to 2 "29. Trans lucent; vitreous. White, grey, and rarely green or blue. C.c.: 37 silica, 31 "8 alumina, 19 2 soda, 47 sodium, and 7 3 chlo rine. Greenland, Vesuvius, Ilmen Hills, Fredriksvarn, and Litchfield in Maine. 509. NOSEAN, 3(AlSi + NaSi) + NaS. Cubic ; and granular. H. = 5-5; G. -2-28 to 2 40. Trans- ^ lucent ; vitreous to resinous. Ash or yellowish grey, sometimes blue, brown, or black. C.c.: 36 silica, 31 alumina, 25 soda, and 8 sulphuric acid. Lake Laach, and Rieden near Andernach. on the Rhine. Occurs in phonolites, in minute crystals. 510. HAUYNE, 2(AlSi + NaSi) + CaS. Cubic; chiefly ooO ; also fig. 487; but more common in grains. Cl. ooO. H. =5 to 5 5; G. =2 4 to 2 5. Semitransparent or trans lucent; vitreous or resinous. Azure- or sky-blue; streak bluish white. C.c.: 34 2 silica, 28 5 alumina, 11 5 soda, 4 3 potash, 10 4 lime, and ll l sulphuric acid. Vesu vius, Mount Vultur near Melfi, the Cam- pagna of Rome, and Niedermendig near Andernach. 511. LAPIS-LAZULI. Cubic ; Ooo ; generally massive, granu lar. H. =5-5; G. -2-38 to 2-42. Trans- Fig. 487 (sp. 510). lucent on edges; dull resinous or vitreous. Ultramarine, or azure-blue; streak light blue. B.B. fuses readily to a white porous glass. In h. acid the powder is dissolved and gelatinizes, evolving sulphuretted hydrogen. C.c.: 45 "50 silica, 5 "89 sul phuric acid, 3176 alumina, 9 09 soda, 3 52 lime, 86 iron, 42 chlorine, 95 sulphur, 12 water. Near Lake Baikal, China, Tibet, Tartary, Monte Somma, and Chili. It is used for ornamen tal purposes, and in the preparation of ultramarine. The colour both in it and hauyne seems due to some compound of sulphur with sodium and iron. MICA GROUP. 512. BIOTITE (Magnesia- Mica), Al.,iSi 3 + (Mg, K, Fe).jSi 3 . Oblique prismatic, C 89" 59 . OP (c), 98 41 P (in), - P (o), o=P c o (b), Poo (r), - f P C 3 (z). Cl. basal, perfect; sectilo; thin plates

elastic. H. =2 5 to 3; G. -2 85 to2 9. Transparent, but often only