HARDWICKE'S SCIENCE-GOSSIP. 



J 95 



Red. — The red specimens are also coloured by 

 ferric oxide, sometimes manganese is also present. 



Spathic Iron Ore. — Composition, FeC0 3 . When 

 pure is white. 



Pink. — The colour of a pink variety of this mineral 

 was found to be due to the presence of a small 

 quantity of manganous carbonate. 



Black. — This mineral was found to be coloured by 

 the presence of carbon. 



Wavellite.— Composition, 3A1„0 3 2P 2 5 I2H 2 0. 

 This body when pure is white. 



Blue. — Erdmaun found in a specimen of this 

 mineral I per cent, of ferric oxide. Turquoise is 

 a blue variety of wavellite, and has been examined 

 by Church, who found 2' 21 per cent, of ferrous oxide 

 and 5*27 of cupric oxide, also by Hermann who 

 found 1 • 10 of ferric oxide and 2*02 of cupric oxide. 

 The colour of the blue wavellite was found to be due 

 to the presence of phosphate of copper, thus it 

 approaches to turquoise in composition. 



Schorl. — The formula of this mineral is very 

 complicated. The name is generally applied to 

 the black varieties of Tourmaline. 



The colour is due to ferrous and ferric silicates ; the 

 combination of the two silicates forming the black 

 colour. 



Muscovite. — (Common Mica). Composition 

 K„H,Al 6 Si 6 O 21 + H 8 Sii O 22 . This mineral when pure 

 is colourless. 



Brown. —The colour of this variety was found to 

 be due to both ferrous and ferric silicates. 



Black. — The colour of this mineral was also due to 

 the two silicates of iron. 



Letidolite. — A variety of mica containing lithuimi, 

 often found colourless. 



Peachblossom Coloured. — This colour is due to the 

 presence of a smaller quantity of manganous silicate. 



Talc. — Composition, Mg 4 Si 5 14 H 2 0. When pure 

 is white. 



Yellow. — The colour of this mineral was found to 

 be due to a small quanty of ferric silicate. 



Red. — This variety is coloured by the presence of 

 ferric oxide. Treatment with hydrochloric acid 

 dissolves the ferric oxide, leaving the talc colourless. 



Black. — Black talc owes its colour to both ferrous 

 and ferric silicates. 



Actinolite.— Composition (Ca, Mg, Fe), Si0 3 . 



Green. — It will be seen from the composition of 

 the mineral that it owes its colour to ferrous silicate, 

 which is a component of the green mineral. 



Asbestos.— Composition, CaSi0 8 3MgSi0 3 . When 

 pure is white. 



Green. — This mineral is coloured by the presence of 

 ferrous silicate, which replaces the ether silicates to a 

 certain extent. 



Greyish-Green. — Is also coloured by th . presence of 

 ferrous silicate. 



Epidote. — Formula very complicated. 



Green. — This mineral contains ferrous silicate as an 



essential ingredient, therefore the colour is due to that 

 body. 



Axinite. — Formula very complicated. 



Greyish. — This mineral was coloured by the 

 presence of both ferrous and ferric silicates. 



Serpentine.— Composition, MgSi0 3 , Mg 2 Si0 4 

 2H 2 0. When pure is white. 



Green. — The colour of this variety of the mineral is 

 due to ferrous silicate, which varies in amount from 

 one to fourteen per cent. 



Red. — The colour of the red variety of serpentine 

 is due to ferric oxide. 



Garnet. — Formula variable. Pure garnet is 

 white. 



Dark-red. — The colour of dark-red garnet is due to 

 both manganous and ferric silicates, ferrous silicate is 

 present in some and perhaps slightly modifies the 

 colour. 



Hypersthene. — Composition, (MgFe) Si0 3 . 



Green. — It will be seen from the formula that the 

 colour of this mineral is due to ferrous silicate, which 

 is a constituent of the mineral. 



Stilbite. — Composition, CaAl 2 Si 6 16 5H 2 0. 

 When pure is white. 



Red. — Red varieties of stilbite are coloured owing 

 to the presence of both manganous and ferric silicates 

 which replace to a certain extent the silicates which 

 are the real components of the mineral. 



Steatite. — Composition 3 Mg Si O s , H 2 Si 3 . 

 When pure is white. 



Bluish- Green. — The colour was found to be due to 

 ferrous silicate. 



Augite. — Composition (Ca Mg Ee) Si 3 . 



Black. — The black varieties owe their colour to 

 both ferrous and ferric silicates. 



Felspar. — Composition K 2 O, A1 2 3 , 6 Si O z . 

 When pure is white. 



Red. — The colouring varying from flesh-red to 

 very dark red is due to varying amounts of ferric 

 oxide. 



On looking at the results of these analyses we find 

 that the colouring agents are very few in number ; 

 viz. carbon, cobalt salts, manganous salts, ferric 

 oxide, hydrate, and silicate, and ferrous salts, the 

 presence of organic matter other than carbon is very 

 doubtful. The above may be arranged as 

 follows : — 



Pink colours are produced by Manganous and 

 cobalt salts. 



Red colours are produced by Ferric oxide, man- 

 ganous and ferric silicates. 



Yellow colours are produced by Ferric hydrate and 

 silicate. 



Brown colours are produced by Ferric oxide and 

 silicate. 



Green colours are produced by Ferrous silicate. 



Blue colours are produced by Copper salts. 



Black colours are produced by Carbon, and Ferrous 

 and ferric silicates. 



K 2 



