30 PHYSIOGRAPHY. 



Manganite Margarite. 



Massive : composition granular, or columnar. the latter 

 more frequently. 



1. It is infusible before the blow-pipe, and colors glass of borax, violet- 

 blue. It is insoluble in nitric acid. In heated sulphuric acid, it dis- 

 engages chlorine. Also, before the blow-pipe, or alone, in a strong heat, 

 it gives out oxygen. 



2. Analysis. 

 By TURNER. 



Protoxide of manganese - - - - - SO 92 

 Oxygen 8-98 



Water - - 10-10 



3. Manganite occurs in abundance, and great beauty, at Ihlefeld in 

 the Hartz, and at Oehrenstock near Ilmenau in Thuringia. 



MARCELLINE. (See Black Manganese.) 

 MAREKANITE. (See Pitchstone.) 



MARGARITE. Rhombohedral Pearl-Mica-. 

 MOHS. 



Primary form. Rhomboid, of unknown dimensions. 



Secondary form. Hexagonal plates. 



Cleavage, parallel with the bases of the hexagonal plates, 

 highly perfect; also traces parallel with the sides of such 

 plates. Fracture not observable. Surface of bases trian- 

 gularly streaked, of sides horizontally streaked, though 

 faintly. 



Lustre, common pearly upon the bases of the hexagonal 

 tables, both in faces of crystallization and of cleavage; vit- 



oftcn approaches to 4-7. It is important to observe, that the exterior 

 strata of large crystals sometimes afford a black streak, and show low 

 degrees of hardness, while the interior parts still offer the characters in- 

 dicated in the preceding description. It would seem, therefore, that the 

 difference in several of these properties, is owing to a change or decom- 

 position of the substance itself, which does not affect the regular form.. 



