PHYSIOGRAPHY. 



Helvin. 



255 



3. It is found at Langbahshytta in Sweden, where it forms narrow 

 veins in a beautiful red, manganesian Pyroxene, and a granular brown 

 Garnet. 



HELIOTROPE. (See Quartz.) 

 HELVIN. Tetrahedral Garnet. MOHS. 

 Primary form. Tetrahedron. 

 Secondary form. 



Fig. 239. 



Cleavage, traces of the octahedron. Fracture uneven. 

 Surface, P smooth, and a little rounded, sometimes streak- 

 ed parallel to the edges, a rough, but even. 



Lustre vitreous, inclining to resinous. Color wax- 

 yellow, inclining to honey-yellow, and yellowish brown, or 

 to siskin-green. Streak white. Translucent on the edges. 



Hardness =6-0 . . . 6-5. Sp. gr. = 3-100. 



1. Before the blow-pipe, upon charcoal, it melts in the reducing 

 flame with effervescence into a globule, of almost the same color as the 

 mineral. In the oxidating flame, the color becomes dark, and the fusion 

 more difficult. With borax, it yields a transparent glass, often colored 

 >y manganese. 



2. Analysis. 

 By VOGEL. 



Silica .... 39-50 



Alumina .... 15-65 



Oxide of iron .... 37-75 

 Oxide of manganese . . . 3-75 

 Lime 0-50 



