i 9 4 



HARD WICKE ' S S CIE NCE- G SSI P. 



On examination of specimens of this mineral, it was 

 found that they became colourless on heating, 

 cracking to pieces, and yielded a small quantity of 

 a liquid containing no ammonium carbonate as stated 

 by Foster : it was, in fact, water. On further 

 examination the colour was found to be due to 

 disseminated ferric hydrate, which decomposed on 

 heating, giving up its water. 



Cornelian. — A variety of quartz. 

 Red. — The colour is due to ferric oxide. 

 Beelsite. — A variety of chalcedony. The colour 

 of a red variety of this mineral was also due to ferric 

 oxide. 



Jasper. — Another variety of quartz, occurs of 

 various colours. 



Red. — The colour of the red specimens is due to 

 ferric oxide. 



Yellow. — Yellow jasper is coloured by ferric 

 hydrate. 



Flint. — Many specimens of this mineral were 

 examined ; the colour of red, brown, grey, and black 

 flint was found to be due to the presence of a small 

 quantity of ferric oxide, and the yellow and brownish- 

 yellow to ferric hydrate. 



Opal. — Composition Si 2 with water. When pure, 

 is white. 



Red. — A red variety of this mineral was coloured 

 by the presence of ferric oxide. 



Blende. — Composition MS. Pure zinc sulphide is 

 white. 



Black. — The colour of the black variety of this 

 mineral is due to ferrous sulphide. Various analysts 

 have found iron to the amount of I*i8 to 14*32 per 

 cent. ; the iron occurs as ferrous sulphide, and thus 

 gives the mineral a black colour. 



Common Salt. — Composition Na Ce. When pure, 

 is colourless or white. 



Pink. — The colour of a pink variety of this salt was 

 found to be due to a small quantity of manganous 

 chloride. 



Red. — The red variety owes its colour to enclosed 

 ferric oxide or a reddish clay, which occurs in the 

 salt formations. 



Fluor Spar. — Composition Ca F 2 . This substance 

 when pure is colourless or white, but as a mineral it 

 occurs in all colours. 



Purple Fluor. — The various colours of fluor spar 

 have been attributed to organic matter, and to the 

 molecular structure of the mineral. Schrotter found 

 in- the dark blue fluor of Wolsendorf, Bavaria, 0*02 

 per cent, of ozone, which Schonbein has shown to be 

 antozone, and he gave the name antozonite to this 

 mineral. Schafhautl found in this fluor 0*02073 per 

 cent, nitrogen; 0*00584 hydrogen; 0*0365 carbon; 

 and 0*08692 chloric acid. Wyrouboff also examined 

 the mineral and found in it 0*0025 carbon ; 0*0038 

 hydrogen, with 0*0180 alumina ; 0*0032 ferric oxide ; 

 0*0025 ferrous oxide, and 0*007 °f chlorine. 

 Wyrouboff attributes the colour to compounds of 



carbon and hydrogen derived from the water that 

 deposited the fluor spar. 



The following results were obtained on examina- 

 tion of several specimens : — 



On powdering one of the specimens it gave a very 

 peculiar odour, but it was gone instantly. This is 

 somewhat like the one examined by Schrotter, as it 

 is stated that the odour from it is so powerful as to 

 cause headache and giddiness in the miners who work 

 amongst it. 



On heating, the mineral gives a very beautiful violet 

 fluorescence, and the fluor becomes first violet and 

 then quite colourless. They all contained manganese, 

 but no organic matter. The manganese was present 

 as fluoride. 



From these results it is difficult to say to what the 

 colour is really due. It certainly is not due to 

 organic matter, and the manganous fluoride detected 

 in it, though of a violet colour, is not dark enough to 

 give the purple colour to the fluor-spar. This must 

 be left for further experiment. 



Green Fluor-spar also gave a violet fluorescence on 

 heating, and the colour was found to be due to a 

 small quantity of ferrous silicate. 



Yellow Fluor-spar is coloured by the presence of 

 ferric hydrate. On heating, this mineral becomes red. 

 Gypsum.— Composition, CaS0 4 2H 2 0, when pure 

 is colourless or white. 



Red varieties of this salt are coloured by ferric oxide. 

 Websterite. — When pure is white. 

 Yellowish-brown. — The colour of a yellowish-brown 

 specimen was found to be due to ferric hydrate. 



Calcite. — Composition, CaC0 3 . When pure is 

 colourless or white. 



Yellowish-red. — A yellowish-red variety was found 

 to owe its colour to ferric hydrate. On heating it 

 cracks to pieces and becomes brown. 



Peachblossom Coloured.— -The colour of this specimen 

 was found to be due to cobalt carbonate. 



Pink Calcite.— A pink variety of marble on exa- 

 mination showed that the colour was due to 

 manganous carbonate, of which it contained 0*37 per 

 cent. Specimens of this variety of marble have 

 before been examined by Roue, who found 1 • 13 per 

 cent, of manganous carbonate, and a specimen from 

 Nantlle Valley, Carnarvonshire, contained as much 

 as 8 per cent, of the same. 



Black. — Bischof found in a black limestone 1*15 

 per cent, of ferrous carbonate. 



Upon ignition this marble becomes quite white, 

 and the colour is due to disseminated carbon, which 

 burns off on heating. 



The presence of ferrous carbonate in the limestone 

 examined by Bischof, is not sufficient to explain the 

 black colour. 



Aragonite. — Composition, CaC0 3 . When pure is 

 colourless or white. 



Yellowish-red. — A yellowish-red variety of this 

 mineral was coloured by ferric oxide. 



