182 DESCRIPTIONS OF MINERALS. 



usually contain much phosphorus, from organic sources, 

 and hence the iron afforded is best fitted for castings. Li- 

 monite is also pulverized and used for polishing metallic 

 buttons and other articles, As yellow ochre, it is a common 

 material for paint. 



Gotldte {Pyrrliosiderite, LepidokroMte) is another iron hydrate, often 

 in prismatic crystals, as well as fibrous and massive, of the formula Fe 

 4 H 2 (=Fe 3 + H 2 0), and G. =4 '0-4 -4. 



TurgiU has the formula Ee0 7 H 2 =2Ee0 3 + H 2 0. Xanthotiderite 

 and limnite are other related hydrates. 



Melanterite.— Copperas. Iron Vitriol. Green Vitriol. 



Monoclinic. In acute oblique rhombic prisms. I A i"= 

 82° 21'; A 7=80° 37'. Cleavage parallel to perfect. 

 Generally pulverulent or massive. 



Color greenish to white. Lustre vitreous. Subtranspa- 

 rent to translucent. Taste astringent, sweetish, and metal- 

 lic. Brittle. H.=2. G. = l-83. 



Composition. Fe0 4 S-f7aq = Sulphur trioxide 28*8, iron 

 protoxide 25*9, water 45 -3— 100. B.B. becomes magnetic. 

 Yields glass with borax. On exposure, becomes covered 

 with a yellowish powder, which results from oxidation. 



Obs. This species is the result of the decomposition of 

 pyrite and pyrrhotite, which readily afford it if moistened 

 while exposed to the atmosphere, and it is obtained from 

 these sulphides for the arts (p. 173). An old mine near 

 Goslar, in the Hartz, is a noted locality. 



Copperas is much used by dyers and tanners, on account 

 of its giving a black color with tannic acid, an ingredient in 

 nutgalls and many kinds of bark. It for the same reason 

 forms the basis of ordinary ink, which is essentially an in- 

 fusion of nutgalls and copperas. It is also employed in the 

 manufacture of Prussian blue. With potassium ferrocya- 

 nide, any soluble salt of iron sesquioxide, even in minute 

 quantity, gives a fine blue color to the solution (due to the 

 formation of Prussian blue), and this is a delicate test of the 

 presence of iron. 



CoquimUte, Copiapite, Voltnitp, Raimondite, Botryogen, Fibroferrite, 

 Illicit?, are names of other hydrous iron sulphates ; and Halotrichite 

 is an iron-alum. 



Jarosite is a hydrous iron-potash sulphate. 



Pisanite is an iron-copper vitriol. 



Lagonite. A hydrous iron borate, from the Tuscan lagoons. 



