110 PHYSIOGRAPHY. CLASS IJ. 



temperature, and is said to remain even after having ex- 

 . posed the crystals to a red heat. 



The union of this and the following species within a 

 single one, which formerly took place in almost all mine- 

 ralogical systems, and even now continues in some of 

 them, is at present gradually giving way. The impossibi- 

 lity of uniting in one series rhombohedral and prismatic 

 forms, or the degrees of specific gravity of the two .sub- 

 stances, would each of them be a sufficient motive for ef- 

 fecting this separation. 



2. The varieties of the present species consist of 

 Oxide of Zinc 66-00. 66.37. 

 Silica 25-00. 26-23. 



Water 9-00. BERTHIEH. 7-40. BERZELIUS. 



Its chemical formula is Zn 3 Si 2 + 3 Aq, which corresponds 

 exactly to the numbers given in the analysis by BERZELIUS. 

 Reduced to powder, it is soluble in heated sulphuric or mu- 

 riatic acid, and when cooled it forms a jelly. Before the 

 blowpipe it decrepitates a little, loses its transparency, 

 intumesces, and emits a green phosphorescent light. It is 

 infusible without addition, but is dissolved by borax into 

 a clear glassy globule, which becomes opake on cooling. It 

 is phosphorescent by friction. 



3. The present and the following species are frequently 

 found accompanying each other in veins, and particularly 

 in beds belonging to various classes of rocks, but chiefly 

 calcareous ones. They are often associated with hexahe- 

 dral Lead-glance, dodecahedral Garnet-blende, and some 

 varieties of Iron-ores. 



4. Considerable quantities occur at Bleiberg and Raibel 

 in Carinthia, Rezbanya in Hungary, Freiburg in Brisgaw, 

 Altenberg near Aix-la Chapelle, near Tarnowitz in Silesia, 

 at Olkuzk and Medziana Gora in Poland, in Siberia, &c. 

 It occurs in Leicestershire, Derbyshire, Flintshire, Somer- 

 setshire, &c. in England, at Wanlockhead and Leadhills- 

 in Scotland, and other places. 



