OADZB VI. AXOTOMOUS TRIPHANE-SPAR. 219 



OBSERVATIONS. 



1. The mechanical composition of the different varieties 

 of the present species has given occasion for dividing it 

 into two sub-species. Individuals and massive varieties cf 

 a granular composition are foliated Prehnite ; while imita- 

 tive shapes and massive varieties exhibiting a columnar 

 composition, are called fibrous Prehnite. 



2. From two analyses, one of them referring to a variety 

 from the Cape by KLAPROTH, and the other to a variety 

 from Reichenbach in the Palatinate by L.AUGIER, it ap- 

 pears that the chemical composition of axotomous Triphane- 

 spar is as follows : 



Silica 43-83 42-50. 



Alumina 30-33 28-50. 



Lime 18-33 20-40. 



Oxide of Iron 5-66 3-00. 



Water 1-83 2-00. 



Potash and Soda 0-00 0'75. 



Before the blowpipe it is transformed into a white frothy 

 scoria, and then melts into a compact coloured globule ; 

 with borax it melts into a transparent bead. In dilute mu- 

 riatic acid it is slowly dissolved, and leaves a flaky residue. 

 It shews electric poles when heated. 



3. Axotomous Triphane-spar is met with in various re- 

 positories. It occurs in veins in primitive mountains, with 

 prismatic Axinite, several species of Augite-spar, with 

 prismatic and tetarto-prismatic F eld-spar, and other spe- 

 cies. It is found in beds with octahedral Iron-ore and some 

 species of the order Pyrites. It is very frequent in trap- 

 rocks of all ages, particularly the newer ones, either in 

 amorphous masses, or in very irregular veins, and in ve- 

 sicular cavities, with various species of the genus Kouph- 

 one-spar, sometimes with octahedral Copper. 



4. It was first brought to Europe by Colonel PREHJJ 

 from the Cape of Good Hope, in bright coloured apple- 



f green varieties. Since that time it has been discovered in 



