Page:Encyclopædia Britannica, Ninth Edition, v. 16.djvu/404

Rh 386 MINERALOGY Ulverston in Lancashire ; specular iron at Tavistock in Devonshire and in Cumberland. Martite seems to be the same substance in pseudomorphs after magnetite ; it occurs in octahedra in Bute, Framont (Vosges), New York, and Brazil. 83. ILMENITE, (Fe,Ti) 2 3. Rhombohedral ; R 86. Crystals rhombohedral and tabular, also in twins. Cl. basal ; fracture conchoidal. H. = 5 to 6 ; G. = 4 66 to 5. Opaque, semimetallic, iron-black to dark brown ; streak black or reddish brown. Sometimes slightly magnetic. B.B. infusible, but with microcosmic salt forms a red glass. Slowly sol. in s. acid when pow dered. C. c. : peroxide of iron, with from 8 to 53 per cent, oxide of titanium. Occurs in metamor- phic rocks. Common in chloritic gneiss in Scotland ; Menaccan (Cornwall), Ilmen Mountains, Salz burg, Egersund (Norway), Arendal, Dauphine (Crichtonite), Massa chusetts ( Washingtonite). 84. ISERINE. Cubic ; in octahedra. Strongly magnetic ; in other respects similar to ilmenite, but occurs in igneous rocks. Common as black iron- sand in Scotland ; Iserweise in Bohemia, Auvergne, Canada, New Zealand. 3. COMPOUNDS OF SESQFIOXIDES WITH PROTOXIDES (SPINELS). 85. MAGNETITE, FeO, Fe 2 3. Cubic (figs. 35, 30, 33, 29, 34, 37, with 40, 41, 36). Hemi- tropes common on octahedral face (fig. 169). Twins (fig. 261). Faces of ooO striated in long diagonal. Often compact and granular. Cl. octahedral ; fracture conchoidal or uneven ; brittle. H. = 5 5 to 6 5 ; G = 4 9 to 5 2. Opaque; lustre metallic. Iron-black to brown; streak black. Highly magnetic ; often polar, forming natural magnets. B.B. becomes brown and non-magnetic, fusing with difficulty. Powder sol. in h. acid. C.c. : 31 protoxide and 69 per oxide of iron; or 72 4 iron, 27 6 oxygen; sometimes with titanic acid. In crystals in Shetland and Sutherland ; also Cornwall and Antrim, Traversella (Piedmont), Tyrol, Styria. Massive at Dannemora and Taberg (Sweden), Norway, Urals, Harz, Saxony, Elba. This is the most important ore in Norway, Sweden, and Russia, and affords the finest iron. 86. MAGNESIO-FERRITE, MgO, Fe 2 3. Cubic (fig. 30). H. =6 to 6 &quot;5; G. = 4 57 to 4 -66. Other characters same as magnetite. C.c. : magnesia 20, peroxide of iron 87. Fumaroles of Vesuvius. 87. JACOBSITE, (MnO, MgO), (Fe 2 3, Mn 2 3 ). Cubic ; 0. Black ; vitreous ; streak red. Nordmark in Sweden. 88. FRANKLINITE, (FeO, ZnO, MnO), (Fe 2 3, Mn 2 3 ). Cubic (figs. 34, 64) ; also granular. Cl. octahedral ; fracture conchoidal; brittle. H. =5 5 to 6 5; G. =5-07. Metallic lustre. Iron-black ; streak reddish brown. Opaque ; slightly magnetic. B. B. infusible, but shines and throws out sparks. On charcoal with soda a deposit of oxide of zinc. Sol. in h. acid with evolution of chlorine. C.c. : about 67 iron oxide, 17 manganese peroxide, 16 zinc oxide. Franklin and Sterling (New Jersey). 89. CHROMITE, FeO, Cr 2 3. Cubic; in octahedra, generally granular-massive. H. =5 5; G. =4 4 to 4 5. Opaque ; semimetallic to resinous. Iron-black to dark brown ; streak reddish brown. Fracture uneven ; sometimes magnetic. B.B. unchanged ; in red. flame becomes magnetic; with borax forms an emerald-green bead. Not soluble in acids. C.c. : 19 to 37 protoxide of iron, to 15 magnesia, 36 to 64 peroxide of chromium, 9 to 21 alumina. Unst (Shetland), Towanrieff (Aber- deenshire), Silesia, Bohemia, Styria, Urals, Turkey, Baltimore, Massachusetts, and Hoboken. The ore of chromium ; used for dyes. Irite is chromite mixed with iridosmium. 90. URANI.VITE (Pitch Blende), UO, U 2 3. Cubic (fig. 30) ; usually massive and botryoidal. H. = 5 to 6 ; G = 6 5 to 8. Lustre pitch-like to submetallic. Colour velvet-black, brownish black, and grey. B.B. infusible. Not sol. in h. acid, but easily in hot n. acid. C. c. : oxides of uranium 80, with a mixture of other oxides. Johann-Georgenstadt, Annaberg, Przibram, Red- ruth in Cornwall. The chief ore of uranium. 91. GAUNITE, ZnO, A1 2 3. Cubic (figs. 166, 30, 33, and with 39, 40). Hemitropes like magnetite. Cl. 0; brittle, with conchoidal fracture. H. =7 5 to 8 ; G. =4 3 to 4 9. Opaque ; vitreous to resinous. Dark leek-green to blue ; streak grey. B. B. unchanged. Unaffected by acids or alkalies. C.c.: 44 oxide of zinc, 56 alumina. Falun, Broddbo, Haddam in Connecticut, and Franklin in New Jersey. Dysluitc contains 42 per cent, sesquioxide of iron ; and Kreittonite contains 24 oxide of manganese. 92. HERCYNITE, FeO, A1 2 3. Cubic; generally granular massive. H. ^7 5 to 8 ; G. =3 9 to 3 95. B.B. infusible. C.c. : oxide of iron 411, alumina 58 9. Ronsberg in the Bohmerwald. 93. SPINEL, MgO, A1 2 3. Cubic (figs. 30, 33, 40 with 26); hemitropes united by face of 0. CL octahedral ; fracture conchoidal. H. =8 ; G. =3 4 to 41. Trans parent to opaque ; vitreous. Black, red, blue, green ; streak white. B.B. infusible and unchanged. C.c.: 28 magnesia, 72 alumina; some with a little iron, and the red varieties some chromium. Varieties are Spinel Ruby when scarlet, Balas Ruby when rose-red ; both often sold as the true ruby, but not nearly so valuable ; when of 4 carats valued at half the price of a diamond the same size. These Fig. 282. Fig. 283. Fig. 284 (sp. 94). come from Pegu (native name Balachan). The violet-coloured is the Alabandinc ruby from Alabandin in Caria, (AsiaMinor). The orange red is the Rubicella. The above also occur at Ceylon, Ava, and Siam. Sapphirine is pale sapphire-blue to greenish or reddish blue ; from Aker in Sweden, Greenland, and North America. Plconaste, dark green or blue to black ; from Candy in Ceylon. Chloro- spinel, grass-green with a yellowish white streak ; from Zlatoust. Water-spinel colour less ; from Ceylos. Picotite is a dark blue chromiferous variety from serpentine. 94. CHRYSOBERYL, G10, A1 2 3. Right prismatic (fig. 284). Twins common, united by a face of Poo (fig. 285, also 156). Cl. brachydiagonal imperfect, macrodiagonal more so; fracture conchoidal. H. =8 5; G. =3 68 to 3 - 8. Transparent or translucent; vitreous. Greenish white, leek-green, and dark emerald- green. B.B. infusible. Not affected by acids. C.c. : glucina20, alumina 80. Brazil, Ceylon, India, the Urals, Haddam in Connecticut. A very valuable gem. It sometimes possesses an opalescent band, which when the stone is cut en cabochon appears as a streak of floating light ; whence it derives its name of Cymo- phane. It is then also called the chatoyant or Oriental chrysolite, and when fine is of extreme value. The emerald-green variety, or Alex andrite, is columbine-red by transmitted light. 4. DEUTOXIDES. 95. RUTILE, Ti0 2. Pyramidal ; prisms dominant. P 84 40 ; Poo 65 35 (figs. 286, 287). Hemitropes common, with axes of halves 114 26. Cl. oo P and oo Poo, perfect. H. -6 to 6 6 ; G. -4 2 to 4 8. Trans parent to opaque ; adamantine lustre. Brown-red, red, pale yellow, and black ; streak yellowish brown. B. B. unchanged ; with borax in the ox. flame forms a greenish, in the red. flame a violet glass. Not affected by acids. C.c. : titanic acid, with some per oxide of iron. Craig- cailleach and Ben-y- Gloe (Perthshire), The Cobbler and Ben-Bheula Fig. 285. Fig. 286. Fig. 287. (Argyllshire), Alps, Limoges, Norway, Brazil. Large crystals at Titanium Mount (Lincoln county, Georgia). Used in porcelain painting, and for tinting artificial teeth. When attenuated crystals are imbedded in rock-crystal they are called Venus hair.