ORDER VIII. OCTAHEDRAL IRON-ORE. 401 



composition granular, of various sizes of individuals, 

 and different degrees of cohesion. If the composi- 

 tion be almost impalpable, fracture becomes flat 

 conchoidal, even or uneven. 



OBSERVATIONS. 



1. The present species used to be divided into Common 

 Magnetic Iron-Ore, and Granular Magnetic Iron-Ore or Iron- 

 Sand. The first of these contains almost the whole of what 

 is comprised within the species, except small octahedral 

 crystals and grains, which occur either solitary in sand, or 

 imbedded in basalt, and will be taken more particular no- 

 tice of afterwards. 



2. HISINGER obtained from a variety of the present species 



Protoxide of Iron 94-38. 



Magnesia 0-16. 



The loss is oxygen, as the mineral contains both protoxide 

 and peroxide of iron, according to BERZELIUS, in the pro- 

 portion of 30-98 to 69-02, expressed by Fe + 2 Fe ; the 

 whole content of oxygen being 28-215. It is infusible be- 

 fore the blowpipe, but assumes a brown colour and loses its 

 attractory power, after having been exposed to a great heat. 

 It is soluble in heated muriatic acid, but not in nitric acid. 

 It may be obtained crystallised, by fusing it ; and crystals 

 are b'kewise often produced in the process of roasting the 

 ore which contains this mineral. 



3. The octahedral Iron-ore occurs always in beds, which are 

 sometimes uncommonly extended, both in length and thick- 

 ness, or imbedded in crystals and grains, in chlorite slate, 

 serpentine, greenstone, &c. The beds are included chiefly 

 in gneiss, mica-slate, clay-slate, hornblende-slate, and chlo- 

 rite-slate, greenstone, or sometimes limestone. It is ac- 

 companied by various species of the genera Augite-spar, 

 Feld-spar, Lime-haloide, &c. also by dodecahedral Garnet, 

 rhornbohedral Quartz, rhombohedral Iron-ore, and other 

 species. Those remarkable and extensive beds in the Ban- 



VOL. II. 2 C 



