108 DIACLASITE; 



tie and often much cracked. H. 2 to 3-5. 



S.G. 2 to 2-3. 



Comp. Mg2 Sl + 3H == magnesia 35-6, 

 silica 40-3, water 24-1=: 100-0. 



Analysis, from Fleims, by von Widter- 

 mann : 



Silica 40-82 



Magnesia .... 36-06 

 Peroxide of iron . . . 0*42 

 Carbonic acid . . .0-59 

 Water . . . . .21-72 



99-61 

 BB decrepitates, becomes opaque, and 

 fuses with great difficulty at the edges : 

 in powder, with borax, forms a transparent 

 colourless glass. 



Localities. The Tyrol, with serpentine. 

 United States at Middlefield ; Texas, Penn- 

 sylvania; and at Bare Hills. Maryland. 

 Name. After Professor Chester Dewey. 

 DiACLASiTE, Hausmann. A mineral with 

 the pale colours of Diallage, passing into 

 brass-yellow, but in composition between 

 Diallage and Hvpersthene Streak greenish- 

 grey. H. 3-5 to 4. S.G. 3-32. 

 Analysis, from Baste, by Kohler : 



Silica 53-74 



Magnesia . . . „ 25 09 

 Lime ..... 4-73 

 Protoxide of iron . . 11-51 

 Protoxide of manganese , 0*23 

 Alumina . . . .1-34 

 Water 3-76 



100-40 . 



Locality. Wurlitz in Bavaria. Guadar- 

 rama mountains in Spain, in gneiss. 



Name. From ^'«. y^Xot-u), to cleave through. 



DiADOCHiTE, Breithaupt. A variety of 

 Pitticite in which sulphuric acid is associ- 

 ated with the phosphoric acid. Resembles 

 Iron Cinder in outward appearance ; reniform 

 or stalactitic, with a curved lamellar 

 structure. Colour yellow or yellowish - 

 brown, with a resinous lustre inclining to 

 vitreous. Somewhat translucent. Streak 

 ^mcoloured. Fragile. Fracture conchoidal. 

 H. 3. S.G. 2-03. 



Comp. Phosphosulphate of iron, or (Fe 



P3 + 8H)+4(#eS + 6H.) 

 Analysis by Plattner : 



Peroxide of iron . . . 39-69 

 Phosphoric acid . . • 14-81 

 Sulphuric acid . . . 15-15 

 Water ..... 30-35 



100-00 



DIALLAGE. 



BB colours the flame green, and fuses at 

 the edges, with intumescence, to a black, 

 slightly magnetic enamel. With the fluxes 

 gives the reaction of iron. 



Boiling water extracts 12-6 per cent, of 

 sulphuric acid without any peroxide of iron, 

 leaving 2-3 per cent. 



Localities. Near Grafenthal and Saal- 

 field in Thuringia; in alum-slate. • 



Brit. Mus., Case 56. 



DiAGOisriTE, Breithaupt. See Brew^s- 



TERITE. 



DiAKLASE. See Diaclasite. 



Diallage, Haiiy. A variety of Augite, 

 including Bronzite and Schiller-spar (in 

 part). Oblique. The crystals are usually 

 thick and stout. Colour various shades of 

 green, grey and brown. Lustre vitreous, 

 sometimes pearly. Transparent at the edges, 

 or opaque. Streak white-grey. Structure 

 laminated, with cleavage parallel to the sides 

 and diagonals of a slightly rhombic prism. 

 Brittle, Fracture conchoidal — uneven. 

 Yields to the knife. H. 5 to 6. S.G. 3-11 

 to 3-22, 



Comp. R Si, or one atom of silica to each 



atom of base, R consisting of lime, magnesia, 

 protoxide of iron, protoxide of manganese, or 

 even soda in variable proportions. There is 

 also generally present from 1 to 4 per cent, 

 of alumina, which usually replaces silica, 

 and enters into the composition without 

 changing essentially the crystallization ; 

 and 5 to 4 per cent, of Avater. 



Analysis, from the Gabbro of Prato, near 

 Florence, by Kohler : 



Silica 53-20 



Lime 19*09 



Magnesia .... 14-91 

 Protoxide of iron . . 8-67 

 Protoxide of manganese . 0-38 

 Alumina .... 2-47 

 Water 1-77 



100-49 



This gives nearly the formulae 30(Ca Mg 



Fe) si + Al Si2 + 2H. 



BB on charcoal, fuses with difficulty at 

 the edges to a grey slag ; with borax forms 

 a glass coloured with iron. 



Localities. General!}^ occurs with serpen- 

 tine, or forming a constituent of diallage 

 rock. It is found in the serpentine of the 

 Lizard district in Cornwall, and in the ser- 

 pentine of Portsoy in Banffshire. Landlefoot, 

 near Ballantrae. in Ayrshire. The Alic Hills 

 of Aberdeenshire. Baste in the Forest of 



