Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/441

MINERALOGY 423 intersecting individuals fall nearly into one plane, presenting the form fig. 570 ; when long, fig. 190. Brittle ; fracture uneven. H. =4-5; G. =2-15 to 2 2. Gelatinizes in h. acid. C.c.: silica 48 "6, alumina 20 - 2, lime 7 3, potash 6 "2, water 17 7. Giant s Causeway, Giessen, Marburg, Cassel, Capo di Bove, Vesuvius, Iceland. 617. HAIIMOTOMK, A:lSi 3 + BaSi 2 + 5H . Oblique prismatic, C 55 10 . oo? (.9) ; ooP oo (b) ; OP () Forms like phillipsite, but more frequently in simple twins. Physical properties like phillipsite, but G. =2 3 to 2 5, and fuses Fig. 572. Fig. 571. Fig. 573. Fig. 574. with difficulty. Difficultly sol. in h. acid. C.c. : 46 5 silica, 15 9 alumina, 237 baryta, and 13 9 water. Strontian, transparent (Morvenite, fig. 572) and opaque (figs. 571, 573); Glen Arbuck (fig, 574) and Bowling in Dumbarton ; Corstorphine near Edinburgh ; Audreasberg, Kongsberg, Oberstein. 618. STILBITE, AlSi 3 + CaSi s Oblique prismatic, but with right prismatic habit ; C 50 49 - o-Poo (a) ; oopoo(&) ; P (r) ; ooP2 (m) ; OP (p). Cl. a, perfect. H. =3 5 to 4 ; G. =21 to 2 2. Transparent ; vitre ous. Pearly on a. Colourless, white, yellow, pale brown, brick-red. Decomposed by h. acid, leaving silica. C.c. : silica 57 5, alumina 16 4, lime 8 9 water 17 2. Storr and Talisker in Skye (a, b, p) (fig. 575), and in Hebrides (colourless) ; Arran and Kilmalcolm (pale brown) ; Long Craig (Dumbarton) and Kinneff (Kincardine) (brick-red) ; Iceland, Faroes, Andreasberg,Vindhya Mountains, Wellington Mountains (Australia), Nova Scotia. 619. PUFFLERITE, AlSi 3 + Ca.,Si 3 + 5H-. Fibrous globular concretions, with vitreous surface. H. = 4; G. =2-21. Greyish white. Transparent. C.c. : silica 52 - 8, alumina 16 3, lime 11% water 17 2. Pufflatsch in the Seisser Alp. 620. EDINGTONITE, 4A-lSi 2 + 3BaSi + 12Jf . Pyramidal ; hemihedral with inclined faces. P 87 129 8 ; ooP (a) ; polar edges P 92 51 (fig. 576). Cl. a, per fect ; fracture uneven. H. = 4 to 4-5; G. =27 to 271. Trans lucent ; vitreous. Colourless. C.c.: silica 37 3, alumina 2375, baryta 26 "52, water 12 46. Kil- patrick Hills in Dumbarton shire. 621. FORESITE, 2AlSi. 2 , Ca 3 )Si 2 + 6H. Fig. 575, (sp. 618). Fig . 575 ( sp _ 62 o). Right prismatic. oopoo ; ooPoo ; OP. Cl. brachydiagonal, perfect; lustre thereon pearly. G. =2 4. White. C.c. : silica 50, alumina 27 4, lime 5 "5, soda 1 4, water 151. San Piero in Elba. 622. NATROLITE, AlSi 2 + NaS i + 2H . Right prismatic. ooP (m) 91" ; P (o) ; polar edges 148 20 and 144 40 , middle edge 53 20 ; ooPoo (b) ; ooPoo (a). Radiating acicular crystals, often fibrous. Cl. ooP, perfect. H. =5 to 5*5; G. =217 to 2 26. Pellucid; vitreous. Colourless, ochre-yellow, reddish. Is not pyro-electric. B. B. melts quietly to a clear glass, colouring flame yellow. Sol. in oxalic acid. C.c. : 47*2 silica. Fig. 577. Fig. 578. 27 alumina, 16 3 soda, 9 4 water. Glen Farg (fig. 577), (colourless and reddish), Tantallon Castle (fig. 578), Dumbarton, Bowling (green), Campsie, Bishopton, Glenarm and Port Rush (Ireland), Auvergne, Hesse, Hohentwiel in Swabia, Norway. Crocalite is red, fibrous, and investing ; Kintyre, Forfarshire, Wemyss Bay. and the Urals. 623. SCOLECITE, AlSi 2 + CaSi + 3H . Oblique prismatic, C 89 6 . ooP (m) 91 35 ; P (o) 144 20 ; - P. Prismatic and acicular crystals. Twins common, on face oo P c oo , one face with feathered striae. Cl. ocP, perfect. H. =5 to 5 5; G. =2-2 to 2 3. Pellucid; vitreous; pyro-electric. White to reddish white. B. B. twists in a vermicular manner; melting readily to a porous glass. Only par tially sol. in oxalic acid. C.c. : silica 45 8, alumina 26 2, lime 14 3, water 137. Staffa ; Loch Screden, Mull; Talisker, Skye ; Berufiord, Iceland (fig. 579); Faroes ; Vindhyas, India. Natrolite and scolecite pass into one another. There are two definite in termediates Fargite, consisting of two equivalents of natrolite and one of scolecite, and Mesolitc, consisting of one of the former and two of the latter. The first of these occurs at Glen Farg and at Bishopton (Galactitc) ; the second is the ordi nary radiated zeolite of the amygda- Fig. 579. loids of the Tertiary igneous rocks of the Hebrides and the Faroes. It there occurs in matted crystals of extreme tenuity (Cotton- stone], also in delicate feathery tufts ; in Renfrewshire in spheres with an internally radiated structure, and also in needle form and in downy tufts. 624. GISMONDIKE, AISi + CaS i + 4 H . Pyramidal. P (b) 92 30 ; polar angle 118 580). Cl. P. H. =5, on edges and angles 5 to 6 ; G. = 2 26. Translucent ; vitreous. Bluish white to pale red. C.c : silica 35 9, alumina 27 3, lime 131, potash 2 8, water 211. Island Mageeand Larne, Ireland; Vesu vius, Aci-Castello, and Capo di Bove; Schiffenberg near Giessen: Schlauroth near Gorlitz. 625. ZEAGONITE, AlSi-f(CaK) Si-Mft. Right prismatic. P polar angle 120 37 and 121 44 ; middle angle 89 13 . Crystals like fig. 419. H. =5, on edges and angles 7 ; G. = 2 "2. Transparent ; vitreous. Colourless, white, or bluish. C.c.: silica 44, alumina 23 3, lime 5 3, potash 111, water 15 3. Capo di Bove. 626. THOMSONITE, 2 Right prismatic. ooP (?n) 90 26 ; ooPoo (a}; ooPoo (I) ; iPoo (y); Poo (r) ; ^Poo (x). x : x 177 34 20". Cl. macrodiagonal and brachy diagonal, both perfect. H. -5 to 5 5 ; G. =2 35 to 2 38. Translucent; vitreous ; pearly on mac rodiagonal. Colourless. 15. B. difficultly fusible with intumescence to a white enamel. Sol. with gelatinization in h. acid. C.c. : silica 387, alumina 30 8, lime 13 4, soda 4 4, water 131. Lochwinnoch, Renfrew ; Kilpatrick (fig. 58 01 > Quiraing and Taliskur (sometimes Fi

62 6).