Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/416

398 MINERALOGY to red or blackish brown on exposure. B.B. infusible, but becomes black and magnetic ; with borax and salt of phosphorus shows reaction for iron ; with soda often for manganese. In acids soluble with effervescence. C.c. carbonate of iron, with 62 1 protoxide of iron and 37 9 carbonic acid, but usually 5 to 10 or even 25 protoxide of manganese, 2 to 15 magnesia, and O l to 2 lime. Unst, Kintyre. In beds or masses in Beeralston in Devonshire, Alston Moor in Cumberland, and in many of the tin-mines in Cornwall, in Styria, Carinthia, and Westphalia ; in veins in Anhalt and the Harz ; also in the Pyrenees and the Basque provinces of Spain, as near Bilboa ; in crystals at Joachimsthal, Freiberg, Klausthal. Clay Ironstone, grey, blue, brown, or black, G. =2 8 to 3 5, H. = 3 5 to 4 5, is an impure variety. 278. DIALOGITE (Red Manganese), MnC . Hexagonal rhombohedral ; R 106 56 . Crystals often curved, lenticular, or saddle-shaped ; also spherical, reniform, and columnar orgranular. Cl. R, perfect. H. = 3 5to4-5; G. = 3 3 to3 6. Trans lucent ; vitreous or pearly. Rose-red to flesh-red ; streak white. C.c. : 62 manganese protoxide and 38 carbonic acid. Freiberg, Schemnitz, Kapnik, Nagyag, Elbingerode, and near Sargans. 279. COBALTSPATH, CoCo . Rhombohedral and spheroidal. H. =4 ; G. =4 to 4 13. Peach- blossom-red ; but dark externally. Schneeberg. 280. SMITHSONITE (Calamine), ZnC. Hexagonal rhombohedral ; R 107 40 . Usually reniform, stal- actitic, and laminar or granular. Cl. R, perfect, but curved; fracture uneven, couchoidal ; brittle. H. =5 ; G. =4 1 to 4 5. Translucent or opaque ; pearly or vitreous. Colourless, but often pale greyish yellow, brown, or green. C.c.: 64 8 zinc oxide and 35 2 carbonic acid. Mendip in Somersetshire, Matlock in Derbyshire, compact at Alston Moor, Chessy near Lyons, Altenberg near Aix-la-Chapelle, Brilon in Westphalia, Tarnowitz in Silesia, Hungary, Siberia. 281. ARAGONITE, CaC. Right prismatic. ooP 116 10 ; Poo 108 26 . The most common combinations are ooPoo (h), ooP (M), Poo (k, P) (fig. 275), generally long prismatic (like the separate crystals in fig. 184) ; ooPoo , ooP, OP, generally short prismatic ; crystals of 6P, ooP, Poo , 6Poo (q) (fig. 373) acute pyramidal. But simple crystals are rare, from the great tendency to form twins, con joined by a face of ooP, and repeated either in linear arrangement (fig. 185) or in rosette group ing (fig. 186). Also columnar, fibrous, and in crusts, stalactites, and other forms. Cl. brachy- diagonal, distinct ; fracture conchoidal or uneven. H. =3 5 to 4 ; G. =2 "9 to 3 (massive 27). Trans parent or translucent ; vitreous. Colourless, but yellowish white to brick-red ; also light green, violet-blue, or grey. In the closed tube, before reaching a red heat, it swells, and falls down into a white coarse powder, evolving a little water. Unst and Leadhills ; Valencia, Molina and else where in Aragon ; Leogang in Salzburg, and Anti- paros. Flos-ferri, coralloid, in the iron-mines of Styria. Satin-ymr, fine fibrous silky, at Dufton (Westmoreland). Stalactitic, coast of Galloway, Leadhills, Buckinghamshire, and Devonshire. Also deposited as tufa by the Carlsbad and other hot springs. 282. WITHERITE, BaC. Fig. 37?. Right prismatic. ooP (<-/) 118 30 ; 2Poo(P) 112. Crystals not common like fig. 275, but generally with quite an hexagonal aspect from being twinned like aragonite (fig. 374). Oftener spherical botryoidal, or reniform, with radiated-columnar structure. Cl. oo P, distinct ; fracture uneven. H. =3 to 3 5 ; G. = 4 2 to 4 3. Semitransparent or translucent ; vitreous, or resinous on the fracture. Colourless, but generally yellowish or greyish. B.B. fuses easily to a transparent globule, opaque when cold ; on charcoal boils, becomes caustic and sinks into the support ; soluble with effervescence inn. or h. acid. C.c.: 22 3 carbonic acid and 777 baryta. Alston Moor and Hexham in Northumberland, also in Styria, Salzburg, Hungary, Sicily, Siberia, and Chili. Fig. 374. 283. ALSTONITE, BaC + CaC. Right prismatic. ooP 118 50 ; 2Poo 111 50 ; usual combination P, 2Poo, oo P, resembling an hexagonal pyramid (fig. 375). Cl. ooP to 4-5 ; G. =3-65 to 376. and ooPoo, rather distinct. H. =4 376. Translucent ; weak resinous. Colourless or greyish-white. C.c.: 66 carbonate of baryta and 34 carbonate of lime. Fallowfield near Hexham, and Alston Moor. 284. STRONTIANITE, SrC . Eight prismatic. ooP 117 19 ; Poo 108 12 . Crystals (fig. 376) and twins like aragonite ; also broad columnar and fibrous. Cl. pris matic along ooP (M). H. =3 5; G. =3 6 to 3-8. Translucent or transparent ; vitreous or resinous on fracture. Colourless, but often light asparagus- or apple-green, more rarely greyish, yellowish, or brown ish. B.B. fuses in a strong heat only on very thin edges, intumesces in cauliflower-like forms, shines Fig. 375 (sp. 283). brightly, and colours the flame red ; easily soluble in acids, with effervescence. C.c.: 30 carbonic acid and 70 stroutia. but often contains carbonate of lime (6 to 8). Strontian in Argyllshire, Suther land, Leogang in Salzburg, Brauns- dorf in Saxony, Hamm in West phalia, the Harz; at Schoharie (N.Y.) and elsewhere in United States (Emmonitc). It is used to produce red fire in pyrotechnic exhibitions. Fig. 376. 285. MANGANOCALCITE, (Mn, Ca, Fe) C . Right prismatic ; in prisms like aragonite, and bears the same relation to dialogite that aragonite does to calc-spar. H. = 4 to 5 ; G. = 3 03. Red or reddish white. Vitreous. Schemnitz. 286. CERUSSITE (Lead Spar), PbC . Right prismatic; isomorphous with aragonite and nitre, ocp (M) 117 14 ; Poo 108 16 ; 2Poo (u) 69 20 ; also OP; P (t); Poo (s); <xPoo (I); o>P3 (e) (fig 377). Twins common (figs. 158, 159, 378, 379). Also granular or earthy. Cl. ooP and 2Poo, rather distinct; fracture conchoidal; easily frangible. H. =3 to 3 5; G. =-6 4 to 6 6. Transparent or translucent ; adamantine or resinous. Colourless and often white, but also grey, yellow, brown, black, rarely green, blue, or red ; streak white. B. B. decrepitates violently, but easily fused and reduced ; soluble with effervescence in n. acid. C.c. . 83 "5 protoxide of lead and 16 5 carbonic acid. Very common. Leadhills, Wanlockhead, Keswick, Alston Moor, Beeralston in Devon shire, St Minver in Cornwall ; Przibram, Mies, and Bleistadt ; ML _j- Sc . Fig. 378. Fig. 379. Tarnowitz, Johann-Georgenstadt, Zellerfeld, Klausthal, and many other places. 287. BARYTO-CALCITE, BaC + CaC. Fig. 380. Fig. 381.

Oblique prismatic, C 69 30 . ooP (m) 84 52 , P (s) 106 54 ,