H VIII. HHOMBOHEDRAL IKOX-OKE. 409 



the nature of these admixtures. Thus lenticular clay iron- 

 ore is very rich, while the columnar variety contains but 

 little iron, and is produced from nodules of common clay 

 iron-stone originally engaged in common clay, which have 

 been converted by the influence of heat from burning coal 

 seams, the one into columnar clay iron-ore, the other into 

 porcelain jasper. The rhombchedral Iron-ore is infusible 

 before the blowpipe, but melts with borax, and forms a 

 green or yellow glass, like pure oxide of iron. It is like- 

 wise soluble in heated muriatic acid. 



3. It occurs most commonly in beds and veins in ancient 

 rocks. Clay iron-ore forms either by itself beds in secondary 

 mountains, or it is included in beds of clay in the shape of no- 

 dules or irregular masses. Rhombohedral Iron-ore occurs iu 

 crystals among the rocks ejected by Vesuvius, and lining the 

 cavities and fissures of lava, where it seems to be a product of 

 sublimation. In beds, it is generally accompanied by other 

 ores of iron, several species of the genera Feld-spar, Augite- 

 spar, and Garnet ; rhomboheural Lime-haloide and rhom- 

 bohedral Quartz ; in veins, the compound varieties are 

 chiefly associated with several varieties of rhombohedral 

 Quartz (such as Iron-flint, &c.), the simple ones in narrow 

 veins in primitive mountains, likewise with rhombohedral 

 Quartz, but moreover with prismatic Feld-spar and Albite, 

 with ores of titanium, &c. 



4. The most distinct crystals, sometimes of considerable 

 size, are found in the island of Elba, along with hexahedral 

 Iron-pyrites and rhombohedral Quartz ; at Framont in 

 Lorraine ; at St Gothard in Switzerland ; in Dauphiny, 

 where they occur in narrow veins in primitive rocks ; 

 in the vicinity of Mount Vesuvius, and in the island 

 of Stromboli. Besides the island of Elba, there occur 

 considerable quantities of this species in Norway and Swe- 

 den, in Stiria, &c. frequently mixed with octahedral Iron- 

 ore. Micaceous Iron-ore is very common in the beds 

 of brachy typous Parachrose-bary te in Stiria and Carinthia. 

 Red Iron-ore is found in Saxony, Bohemia, the Kartz, the 



