24 PHYSIOGRAPHY. 



Anhydrite Ankerite . 



6. The blue varieties, in which the granular particles of composition 

 cohere more firmly than in others, are cut and polished for various or- 

 namental purposes, and are known in the arts by the name of Marmo 

 bardiglio di Bergamo. 



ANHYDROUS SILICATE OF IRON. 



Massive : foliated. 



Cleavage, divides easily into four-sided prisms. 

 Color dark brown, opake. 

 Hardness = 4. Sp. gr. = 3-884. 

 Brittle. Attracted by the magnet. 



1. Heated in a glass-tube, it emits ammoniacal vapors, and loses 1-97 

 of its weight. Alone before the blow-pipe, it is infusible, but in the re- 

 ducing flame acquires a metallic lustre, and assumes the appearance of 

 magnetic iron. Dissolves in muriatic acid by the aid of heat, without 

 effervescing, leaving behind a quantity of silica in flakes. 



2. Analysis. 

 By THOMSON. 



Silica 29-600 



Protoxide of iron . . . 68-605 

 Protoxide of manganese . . 1-857 



3. It is found at Sclavcorrach, one of the Morne mountains, in the 

 north-east of Ireland. 



4. Not enough is known concerning the foregoing mineral to pro- 

 nounce upon its specific character with certainty. It scarcely differs 

 from Yenite except in being aUi^cted by the magnet, and in its infusi- 

 bility. 



ANKERITE. Paratomous Lime-Haloid e. 

 MOHS. 



Primary form. Rhomboid. P on P= 106 12. 



Cleavage parallel with the primary faces perfect. Frac- 

 ture uneven. 



Lustre vitreous, slightly inclining to pearly. Color white, 

 with various tints of grey, red and brown. Streak brown, 

 Translucent, often very faintly. 



Brittle. Hardness = 3-5 . . . 4-0. Sp. gr. = 3-080. 



Compound Varieties. Twin-crystals. Face of com- 

 position parallel with the vertical axes. 



