112 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



IRON. 



Iron Minerals, 

 magnetite. (magnetic iron ore, loadstone.) 



(3oinposition : Fe20:( -+- FeO. Protosesquioxide of irou, coiitainiug 

 iron 72.4 per cent, and oxygen 27.6 per cent. 



It crystallizes in tiie isometric system, especially in octabedrons and 

 dodecahedrons. It commonly occnrs in the crystalline grannlar form, 

 witb grains of varions sizes, or massive. It varies in hardness from 5.5 

 to 6.5, and in specific gravity from 4,9 to 5.2. It has a full metallic lus- 

 ter, and iron-black color. It is always magnetic and sometimes shows 

 polarity. 



Magnetite is a very valuable source of iron. Sometimes it occurs in 

 masses of great purity and furnishes iron of the highest quality. It 

 frequently contains the various sul[)bides of iron, the phosphate of lime, 

 apatite, and titanic acid, and any one or several of these may be pres- 

 ent in sufficient amount to prevent its being utilized. It generally 

 occurs in the older crystalline rocks. To illustrate the occurrence of 

 magnetite five specimens are shown : 



(1) Crystallized, small octaliedrous on luassiTe. O'Neil Miue, Orauge County, 

 New York. (17642.) 



(2) Crystallized, largo octahedrons on massive. Great Western Mine, Iron Springs, 

 Iron County, Utah. (4;?648.) 



(3) Crystalline, granular. Crown Point Mine, Crown Point, Essex County, New 

 York. (65320. ) 



(4) Massive, loadstone. Arkansas. (31'J65.) 



(5) Magnetic sand, from washing alluvial deposit. December 27, 1>H0. White 

 River, Pittsfield, Ruthin 1 County, Vormoiit. (65330.) 



UEMATITE, (RED UEMATITE, SPECULAR IRON, MICACEOUS IRON, 



IRON GLANCE.) 



Composition : FejO^. Sesquioxide of iron, containing iron 70 per 

 cent, and oxygen 30 per cent. 



Crystallizes in the rhombohedral system, crystals being generally 

 rhombohedral or tabular, with rhombohedral faces. It occurs granu- 

 lar, lamellar, n.'assive, and earthy. 



It varies in hardness from 5.5 to 0.5 and in specific gravity from 4.5 

 to 5.3; it is dark steel-gray to reil in color and bright metallic to 

 earthy in luster; is generally opa(iue,but occasionally, in thin crystals, 

 transmits a blood-red light. The i)owdered mineral is always bright 

 red in color. 



Hematite occurs in a variety of forms in rocks of all ages and is a, 

 very valuable source of iron. As an ore it has received a largt^ vaiiety 

 of names, depending for the most i)art upon the physical c(Mi(lil ion of 



