OLIVIA. 

 or greenish-grey. Lustre vitreous to resi- 

 nous. Translucent to opaque. Streak olive- 

 green or brown. Brittle. Fracture con- 

 choidal, uneven. H. 3. S.G. 4-1 to 4-4, 

 Comp. Hydrated arseniate of copper, or 



Cu4 (As, 'P) + Hr=: oxide of copper 58-4, 

 arsenic acid 31-7, phosDhoric acid 6' 6, water 

 3-3 = 100. 



Analysis, from Cornwall, by v. Kohell : 

 Oxide of copper . . .56-43 

 Arsenic acid . . .36-71 



Phosphoric acid . . , 3 36 

 Water . . . .3-50 



100-00 



BB in the forceps fuses, imparts a pale 

 blue colour to the flame, and on cooling, 

 crystallizes to a blackish-brown, radiated 

 mass, with an adamantine lustre and co- 

 vered with a network of prismatic crystals. 

 On charcoal, deflagrates, emits strong arse- 

 nical fumes, and yields a globule which is 

 brow^nisti on the outside, and white in the 

 middle. 



Soluble in nitric acid and in ammonia. 



Localities. The finest specimens of Oli- 

 venite have been found in Cornwall, prin- 

 cipally at Huel Gorland, Ting Tang, Huel 

 Unity, Carharrack, Tincroft, Huel Buller, 

 and at Pednandrea. Bedford United 'lines, 

 near Tavistock, Devonshire. Tyne Head 

 Mine, near Alston, Cumberland. — Foreign. 

 Camsdorf and Saalfeld in Thuringia. The 

 Tyrol. Siberia. Chili, &c. 



Name. Prom its olive-green colour. 



Brit. Mus., Case 56. 



31. P. G. Wall-case 2 (British) ; Horse- 

 shoe Case 922 to 924. 



Olivin, Werner. Olivine, Brooke ^" Mil- 

 ler. Chrysolite of inferior colour and clear- 

 ness, occurring in yellowish-green or olive- 

 coloured, imbedded masses and grains. 

 Lustre vitreous ; sometimes when decom- 

 posing iridescent and somewhat metallic 

 externally. Transparent. Fracture imper- 

 fect-conchoidal. Not so hard as Chrysolite. 

 H, 6-5 to 7. S.G. 3-33 to 3-45. 



Comp. Anhydrous silicate of magnesia, 



or Mg2 Si, but a portion of the magnesia is 

 frequently replaced by protoxide of iron, 

 sometimes to the. amount of 15 per cent. 

 Analysis, from Somma, by Walmstedt : 



Silica 40-16 



Alumina .... 0-10 

 Magnesia .... 44-87 

 Protoxide of iron . . 15'88 



OXKOSIN. 265 



Protoxide of manganese . O'lO 



100-61 

 BB alone infusible ; with borax fuses 

 slowly to a transparent glass, coloured by 

 iron. In a powdered state readily decom- 

 posed by muriatic acid, yielding a jelly. 



Localities. Near the Giant's Causeway 

 in Ireland. In basalt and trap. In trap 

 rock at Arthur's Seat near Edinburgh. 

 Unkel, near Bonn on the Rhine. In trap- 

 tuff at Kapferstein, in Styria. Vesuvius. 

 In lava at Hawaii, and other islands in the 

 Pacific. Thetford and Norwich, Vermont, 

 U. S. in boulders of basalt. 

 Brit. Mus., Case 25. 



M.P. G Horse-shoe Case, Nos. 922 to 924. 

 Upper Gallei-y, Wall-case 1, Nos. 36 to 41. 

 Table-case A in recess 4, Nos. 119 to 121. 



Olivinoid. The name given to a sub- 

 stance occurring in meteorites by Prof C. 

 U. Shepard, from its resemblance to Oli- 

 vine. It is softer than Olivine. H. 5-5 to 

 6. It also differs from that mineral in 

 turning black and fusing easily before the 

 blowpipe ; as well as in being more easily 

 attacked by acids. 

 Ollite. See Potstone. 

 Omphazite, Werner. A foliated leek- 

 green variety of Sahlite, usually containing 

 some iron. It occurs at the Sau Alp, in 

 Carinthia, with granular Garnet ; and at 

 Hof, in Bayreuth, accompanying the Sma- 

 ragdite variety of Plorn blende, to which it 

 bears a close resemblance. 



Onegite. a variety of Gothite, found 

 at Lake Onega, in Siberia. 



Onicolo. a variety of Onyx with a deep 

 brown ground, on which is a band of bluish- 

 white. It differs from true Onyx in a cer- 

 tain blending of the tAvo layers, the lowest 

 of which is always the thinnest. It has 

 often the constitution of a deep coloured 

 Sard, but of an extraordinarily fine texture. 

 It is used for cameos. {Barbot.) Some- 

 times the dark ground is covered with 

 bluish spots, surrounded by milky zones. 

 It is chiefly brought from Bohemia. 



Name. The Nicolo or Onicolo is said to 

 take its name from the Greek ^tyJ^^otcg. 



Onkosin, v. Kobell. A kind of clay of an 

 apple-green or brownish colour, passing 

 into greyish and brownish, and occurring 

 in roundish pieces. Lustre weak, slightly 

 resinous. Translucent. Sectile. Fracture 

 splintery or uneven. H. 2. S.G. 2-81. 



2A1 Si + (K,Mg)Si-i-2H. 

 Analysis, by v. Kobell ; 

 Silica 52-52 



