186 DESCRIPTIONS OF MINERALS. 
posure. Streak uncolored. Lustre pearly to vitreous. Trans- 
lucent to nearly opaque. H.=3-4:5. G.=3-7-3°9. 
Composition. FeO, C=Carbon dioxide 37:9, iron protox- 
ide 62°1=100. Often contains some manganese oxide or 
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 or foliated variety is called 
spathic or sparry iron, because the mineral has the aspect 
of aspar. The globular concretions found in some amyeda- 
loidal rocks have been called spherosiderite because of its 
spheroidal forms. An argillaceous variety occurring in nod- 
ular forms is often called clay wron stone, and 1s abundant 
in coal measures. | 
Diff. This mineral cleaves hike 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 Styria and Carinthia, it 1s 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 Roxbury, near 
New Milford, Conn., in quartz, traversing gneiss; at Ply- 
mouth, Vt., and Sterling, Mass., it is also abundant. It oc- 
curs also at Monroe, Conn.; in New 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. 
Mesitite is an iron-and-magnesium 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, but was little used 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 

