ORDER IV. HEMI-PRISMATIC VITRIOL-SALT. 43 



parent ... translucent. A faint blueish opales- 

 cence sometimes observable parallel to the faces 

 of Pr + QD. 



Rather brittle. Hardness = 2-0. Sp. Gr. = 1-832, 

 of a variety containing about 0-1 of sulphate of 

 copper. Taste sweetish -astringent and metallic. 



Compound Varieties. Stalactitic, botryoidal, re- 

 niform : composition columnar ; if the particles be- 

 come very thin, the lustre approaches to pearly. 

 Massive : composition granular. Pulverulent. 



OBSERVATIONS. 



1. The present species consists of 



Oxide of Iron 25-7- 



Sulphuric Acid 28-9. 



Water 45-4. BERZELIUS. 



It is Fe 8*2 + 12 Aq = 26-19 Oxide of Iron : 29-89 Sul- 

 phuric Acid : 43-92 Water, according to MITSCHERLICH. 

 It is easily soluble in water, and the solution becomes black 

 on being mixed with tincture of galls. If exposed to the 

 open air, it soon becomes covered with a yellow powder, 

 which is Persulphate of Iron. Before the blowpipe it be- 

 comes magnetic, and colours glass of borax green. 



2. In most cases the hemi-prismatic Vitriol-salt is pro- 

 duced by the decomposition of other minerals, particularly 

 of hexahedral and prismatic Iron-pyrites ; and it is there- 

 fore commonly found in such places in which artificial 

 heaps constructed for that purpose, mines or other circum- 

 stances, have given occasion to its formation. It is also 

 found dissolved in the waters of several mines. 



3. It occurs in the Rammelsberg near Goslar in the 

 Hartz, at Schwarzenberg in Saxony, in several mines at 

 Schemnitz in Hungary ; also in Sweden, in Spain, &c. ; in 

 different coal-mines in England ; at Hurlet in Renfrew- 

 shire in Scotland, and other places. 



4. Both the natural and the artificial hemi-prismatic Vi- 



