186 DESCRIPTIONS OF MINERALS. 



posure. Streak uneolored. Lustre pearly to vitreous. Trans, 

 lucent to nearly opaque. H. =3-4*5. G-. =3 -T-3 -9. 



Composition. Fe ; C = Carbon dioxide 37*9, iron protox- 

 ide 62 -1 = 100. Often contains some manganese oxide oi 

 magnesia, and lime replacing part of the iron protoxide. 

 Before the blowpipe it blackens and becomes magnetic ; but 

 alone it is infusible. Dissolves in heated hydrochloric acid 

 with effervescence* 



The ordinary crystallized oi foliated variety is called 

 spathic or sparry iron, because the mineral has the aspect 

 of a spar. The globular concretions found in some amygda- 

 loidal rocks have been called splierosiderite because of its 

 spheroidal forms. An argillaceous variety occurring in nod- 

 ular forms is often called clay iron stone, and is abundant 

 in coal measures, 



Diff. This mineral cleaves like calcite and dolomite, but 

 it has a much higher specific gravity. It readily becomes 

 magnetic before the blowpipe. Heated in a closed glass 

 tube it gives off carbon dioxide, and becomes magnetic. This 

 test distinguishes it from other iron ores. 



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

 often accompanies metallic ores. The largest deposits are 

 in gneiss and mica schist, and clay slate. It is also abundant 

 in the coal formation principally in the form of clay iron 

 stone. In Stvria and Carinthia, it is very abundant in gneiss; 

 and in the Hartz it occurs in graywacke. Cornwall, Alston- 

 moor, and Devonshire are English localities. 



A vein of considerable extent occurs at. Eoxbury, near 

 Xew ITilford, Conn., in quartz, traversing gneiss; "at Ply- 

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

 curs also at Monroe, Conn. ; in Xew York State, in Antwerp, 

 Jefferson County, and in Hermon, St. Lawrence County. 

 The argillaceous carbonate in nodules and beds, is very 

 abundant in the coal regions of Pennsylvania and the West. 



This ore is employed'extensively for the manufacture of 

 iron and steel, 



MesiHte is an iron-and-niagriesium carbonate, Ankerite contains in 

 addition a large percentage of calcium. Like siderite in crystalliza- 

 tion and cleavage. 



General Remarks. — The metal iron has been known from the most 

 remote historical period, bnt was little nsed until the last centuries be- 

 fore the Christian era. Bronze, an alloy of copper and tin, was the 

 almost universal substitute, for cutting instruments as well as weapons 



