PHYSIOGRAPHY. 71 



Native Lead Native Magnesia. 



3. Native Iron, alloyed with Nickel and other metals, forms large me- 

 teoric masses, and enters into the composition of meteoric stones. But at 

 these bodies are regarded as extra-terrestrial in their origin, it will not 

 be proper to describe them in the present work. 



NATIVE LEAD. Lead Melacon e-Me;al. 



Massive. Fracture hackly. 



Lustre metallic. Color pure lead-grey. Streak shining. 



Malleable and ductile. Hardness = 1'5. Sp. gr. = 

 11 '3523. Disagreeable odoj* by friction. 



1. Before the blow-pipe, it melts easily, and is gradually dissipated in 

 fumes, leaving a yellow powder upon the charcoal. 



2. The localities generally quoted of this species, afford it under cir- 

 cumstances, rendering it highly probable that it has been reduced from 

 Galena by heat. Thus, at the island of Madeira it is imbedded in vesi- 

 cular masses, considered as slags by some, and a volcanic rock by others ; 

 and at Alston in Cumberland, associated with Galena Quartz, Minium, 

 and a fused mass resembling slag. But an undoubted deposit of Native 

 Lead exists in Michigan, at Anglaise river, where it occurs in extremely 

 delicate membranes, between the cleavages of galena ; existing, how- 

 ever, only in sufficient quantity to increase the sp. gr. of the Galena to 

 7-83. 



NATIVE MAGNESIA. Rhombohedral Gypsum- 

 Mica. 



Primary form. Rhomboid. 



Secondary form. Low six-sided prisms, rare. 



Massive : composition lamellar, broad columnar, the lat- 

 ter sometimes stellular. 



Cleavage, in one direction perfect. 



Lustre pearly upon the cleavage face. Color white, in- 

 clining to green, grey and blue. Streak white. Translu- 

 cent, sometimes only on the edges. Some varieties lose 

 their transparency on being exposed to the air. 



