Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/435

Rh MINERALOGY 417 (meeting at 141V) less so. H. =6 5 ; G. =2 4 to 2 5. Greenish, greyish, or reddish white to pale red. Translucent ; vitreous or pearly. B. B. melts easily into a porous obscure glass, colouring the flame red. Not affected by acids. C.c. : 78 3 silica, 17 4 alu mina, 3 &quot;2 lithia, and 1 1 soda. Uto, Bolton in Massachusetts, York in Canada. Castor in Elba. Milarite, valley of Milar, Switzerland. 574. RHODONITE (Manganese- Spar), MnSi. Anorthic. oopoo(rt); oopoo (b); OP(c); &amp;lt;P ; P oo ; Po(s); P oo (o) ; m P oo (0: a : b 111 9 ; c : a 93 28 ; n : a 106 19 ; but chiefly massive or granular. Cl. ooPoo and OP, meeting /^ f ^ &quot;V^ &quot;...* at 87 38, perfect ; brittle. II. =5 to 5 5; G. -=3 5 to 37. Translucent ; vitreous or partly pearly. Dark rose-red, bluish red, or red dish brown. Not affected by acids. B. B. fusible. C.c. : 45-8 silica and 54 &quot;2 manganese protoxide, with & 3 to 5 lime and to 6 iron protoxide. St Marcel, L&ngbam Ekaterinburg, the Harz, and New Jersey. Bustamite, pale greenish or reddish grey, with 14 lime, Mexico ; Fowlerite, New Jersey, with 7 to 11 iron protoxide; and Paisbergite, Sweden, are varieties. Hydropite, Photicite, Allagite, and Horn- Manganese are mere mixtures. 575. BABINGTONITE, 9(Ca, Ye, Mn)Si + FeSi 3 . Auorthic. Crystals very low eight-sided prisms, small, attached. g : h 90 24 ; c : a 87 27 ; a : b 112 12 ; b : d 81 8 ; c : d 150 10 (fig. 511). Cl. basal (c), very perfect; also along b. H. =5-5 to 6; G. =3 3 to 3 4. Thin laminae translucent. Splen dent vitreous ; black. Not affected by acids. B. B. fuses easily with efferves cence to a black magnetic bead. C.c. : 507 silica, 11 iron peroxide, 10 3 iron protoxide, 77 manganese protoxide, and 20 - 3 lime, in the Arendal speci mens ; one from Nassau gave about Fig. 511. Tongue (Sutherland), and Gouverneur (New Fig. 512 (sp. 576). B.B. very difficultly 17 of peroxide, with protoxides only 11. Portsoy (Banffshire), Arendal, Nassau, York). 576. SZABOITE, llFeSi 3 -l-2CaSi. Anorthic. o&amp;gt;P (Z); oo P (m) 88 40 ; oopoo(i); ooPw (a); P (p); T (o); 2 P,oo (y) ; 2P oo (&amp;lt;c) (fig. 512). H. = 6 5 ; G. =3 5. Brownish red to reddish yellow. Pleochroic. C.c. : silica 52 4, per oxide of iron 447, lime 3 1. Slightly sol. in s. acid, more so in h. acid. Calvario on Etna, Mont Dore. 577. ANTHOPHYLLITE, 3MgSi + FeSi. Right prismatic. ooP 124 30 . Cl. macrodiagonal, perfect. Clove-brown to purplish brown and leek-green. Trans lucent; radiating and foliated. Pearly on cl. plane. H. = 5 5 ; G. =3 2. C.c. : silica 55 &quot;9, protoxide of iron 167, magnesia 27 8. fusible. Hillswick, Shetland ; Kongsberg and Modum, Norway ; Greenland, and the United States. 578. HORNBLENDE. Oblique prismatic (figs. 513 to 517; see also fig. 192). Distinct cleavage in several directions. H. =4 to 6, but generally 5 (will scratch with knife); G. =2 - 5 to 4 0, but mostly high. Mostly coloured. Lustre vitreous, in some silky or metallic pearly. Sol., but not very readily, in acids; more or less easily fusible. C.c.: anhydrous silicates and aluminates of lime, magnesia, iron pro toxide; more sparingly of soda, yttria, and manganese protoxide. The chief species form by their decomposition highly fertile soils. Amphibole. Oblique prismatic, C 75 10 . ooP 124&quot; 30 , P 148 30 . The crystals short and thick, or long and thin prismatic ; formed especially by ooP (m), ooP c oo (a;), and bounded on the ends chiefly by OP (p) and P (r). Twins common, with the chief axis the twin axis. Very often radiated, fibrous, or columnar, or granular. Cl. prismatic along ooP 124J, very perfect; orthodiagonal and clinodiagonal very imperfect. H. = 5 to 6 ; G. =2 9 to 3 4. Pellucid in all degrees ; vitreous, but sometimes pearly or silky. Colourless or white, but usually some shade of grey, yellow, green, brown, or black. B.B. fuses, generally intumescing and boiling, to a grey, green, or black glass. Those containing most iron are most fusible, and are also partially sol. in h. acid, which scarcely affects the others. C.c. very variable; the silica is partly replaced by alumina, specially in the green or black varieties; RO is chiefly MgO, CaO, and FeO. Lime is the most Fig. 513. Fig. 514 constant element, in most from 10 to 12; magnesia and iron protoxide replace each other, the one increasing as the other diminishes. With 4Si and R = 2Mg + lOa + IFe, the average composition is 53 6 silica, 17 8 magnesia, 12 5 lime, and 16 1 iron protoxide; but Fig. 516. Fig. 517. analyses give 40 to 60 silica, to 17 alumina, to 30 magnesia, 10 to 15 lime, to 36 iron protoxide (or peroxide), and to 4 manganese protoxide, to 8 soda, to 3 potash, and to 1 5 fluorine with a little water. The more important varieties are Amianthiis, Asbestos, and Byssolite, 2MgSi + CaSi. Fine fibrous. White, grey, or green. The fibres often easily separable, elastic, and flexible. Unst, Shinness, Portsoy, Savoy, Tyrol, Corsica. Tremolite, Grammatite, 3MgSi + CaS i, with 58 35 silica, 28 3 9 magnesia, and 13 &quot;26 lime. White, grey, green ; in long prismatic crystals, often striated longitudinally. Pearly or silky ; semi- transparent or translucent. B. B. fuses readily to a white or nearly colourless glass. Loch Shin (Sutherland), Glen Tilt, Gleuelg, Tiree, Cornwall, Cumberland, Sweden, the Alps, Pyrenees, Silesia, Siberia, North America. Nephrite, or Jade, is a tough, compact, fine-grained tremolite, with H. =6 to 6 5 ; G. = 2 9 to 3 1. Fracture close .splintery. Very tenacious. Translucent; dull to resinous. Leek-green to blackish green. Feels slightly greasy. Formerly made into ring-stones, amulets, idols, and war axes. New Zealand, China, Mexico, Peru, Balta (Shetland). Actinolite, Actinote, or Strahlstein (Ua, Mg, Fe) Si. Colour green, inclining to black, grey, or brown. Translucent through out, or only on the edges. Long prismatic crystals, or radiated - columnar masses. B. B. melts to a greenish or blackish enamel. Fethaland and Colafirth and Hillswick (Shetland), Oronsay, Ord Ban (Inverness), Sweden, Tyrol, North America. Hornblende. 6RS i + fiLSij. Green or black, seldomer brown or grey. G. =3 1 to 3 3. B.B. fuses rather easily to a yellow, greenish, or black enamel. Three varieties are distinguished, (a) The noble or Pargasite, pale celadon- or olive-green, and strong pearly or vitreous lustre ; at Pargas in Finland, Tyrie in Scotland. (b) Common hornblende, dark leek- or blackish-green, opaque ; streak greenish grey. A constituent of many rocks, as in Norway, the Alps, and Scottish Highlands (Ballater, Ben Arihaar, Glen- bucket, Colafirth). (c) Basaltic, foliated, with bright even cleavage, opaque, velvet-black ; streak grey or brown. Generally contains alumina (9 to 15) and much (5 to 11) iron peroxide. In basalt and volcanic rocks. Etna, Vesuvius, Rhineland, Bohemia. XVI. C7