163^ Description of Edwardsite. 



Art. XVI. — Description of Edwardsite, a JVew Mineral ; by 

 Charles Upham Shepard, M. D., Prof, of Chem. in the Medi- 

 cal College of the State of South Carolina. 



Mineralogical description. — Primary form. Oblique rhombic 

 prism. M on M=95° (common goniometer.) Base oblique from 

 an obtuse edge. 



Secondary form. The primary, with the acute lateral edges re- 

 placed by single planes inclining to the adjacent lateral faces under 

 137° 30' common goniometer.) In very minute crystals, the sum- 

 mits are occasionally surmounted by four-sided pyramids whose faces 

 correspond to the lateral edges of the prism. 



Cleavage parallel to the bases sometimes distinct, but more com- 

 monly uneven : in the direction of the longer diagonal very perfect. 

 Surface generally not very smooth, but nearly of the same quality 

 on the different faces. 



Lustre vitreous to adamantine. Color hyacinth-red. Streak white. 

 Transparent to translucent. 



Hardness = 4.5. Sp. gr.=4.2 . . . 4.6. 



Chemical description, — Alone before the blowpipe, in very thin 

 fragments, it loses its red color, becoming pearl grey with a tinge of 

 yellow, and fuses with great difficulty on the edges into a transparent 

 glass. With borax, in little fragments, it turns white and gradually 

 dissolves, forming a globule which is bright yellowish green while 

 warm, but colorless when cold. When powdered, it is acted upon 

 very slightly, by aqua regia. A small quantity placed on platinum 

 foil and moistened with sulphuric acid, tinged the flame of the blow- 

 pipe green. 



General observations. — The crystals are rarely above one third 

 of an inch in length by one sixth in breadth. The replacement 

 of the acute lateral edges is deep, imparting to the prism a flattened 

 appearance, except in the case of very minute crystals surmounted 

 by pyramids ; these scarcely exhibit any alteration of the primary 

 prism. The terminations of the larger ciystals are always incom- 

 plete. In some of them, however, the cross cleavage is eminent, in 

 which instances the lateral faces exhibit cross striae parallel with this 

 cleavage, analogous to certain varieties of Hornblende and Pyroxene. 

 The nearest approximations to the value of the angle of inclination 

 between the base and the prism was 100'^ for P on M. More per- 



