IRON ORBS. 247 



compounds. Apatelite is still another, peculiar in containing bat 4 \*i 

 cent, of water. 



Voltaite is a double sulphate of iron, alumina, potash and water, crys- 

 tallizing like alum in octahedrons. From the Solfatara, near Naples. 



spathic iron. — Carbonate of Iron. — Chdlybite. 



T Hexagonal. In rhombohedrous and six-sided prisms, easily 



#cleavable parallel to a rhombohedron of 107°. 

 Faces often curved. Usually massive, with a 

 foliated structure, somewhat curving. Some- 

 times in globular concretions or implanted 

 globules. 



Color light grayish to brown ; often dark brownish-red, or 

 nearly black on exposure. Streak uncolored. Luster pearly 

 to vitreous. Translucent to nearly opaque. H=3 — 4*5. 

 Gr=3*7— 3*85. 



Composition, when pure : protoxyd of iron 62*07, carbonic 

 acid 37*93. Often contains some oxyd of manganese or 

 magnesia, replacing part of the oxyd of iron. Before the 

 blowpipe it blackens and becomes magnetic ; but alone it is 

 infusible. Colors borax green. Dissolves in nitric acid, but 

 scarcely effervesces unless pulverized. 



The ordinary crystallized or foliated variety is called 

 spathic or sparry iron, because the mineral has the aspect of 

 a spar. The globular concretions found in some amygda- 

 loids or lavas, have been called spherosiderite. An argilla- 

 ceous variety, occurring in nodular forms, is often called clay 

 iron stone, and is abundant in the English coal measures. 



Dif. This mineral is foliated like calc spar and dolomite , 

 but it has a much higher specific gravity. It readily becomes 

 magnetic before the blowpipe. 



Obs. Spathic iron occurs in rock of various ages, and 

 often accompanies metallic ores. The largest beds are found 

 in gneiss and graywacke, and also in the coal formation. 

 In Styria and Carinthia, it is very abundant in gneiss, and 

 in the Hartz it occurs in graywacke. Cornwall, Alstonmoor 

 and Devonshire, are English localities. 



A vein of considerable extent occurs at Roxbury, near 

 New Milford, Conn., in quartz, traversing gneiss ; at Ply- 

 nouth, Vt., and Sterling, Mass., it is also abundant. It oc- 



Describe spathic iron. What is its constitution? What are its 

 chemical characters ? How does it differ from calc spar? What are 

 u varieties 1 How does it occur? 



