Hematite Composition,
Crystallization & Structure

Composition. Iron sesquioxide, Fe₂O₃ = Oxygen 30, iron 70. Sometimes with titanium and magnesium., passing into ilmenite.

Crystallization. Hexagonal-rhombohedral. Crystals usually thick to thin tabular. Basal planes prominent, often who wing triangular making (Figs. 257 and 258). Edges of plates sometimes beveled with rhombohedral and pyramidal forms (Fig. 259). Thin plates at times grouped in rosette forms (iron roses) (Fig. 260). More rarely crystals are distinctly rhombolhedral, often with nearly cubic angles.

Structure. Usually earthy or in botryoidally to reniform shapes with radiating structure. At times miraculous; crystallized.

Physical Properties. Rhombohedral parting with nearly cubic angles. H. = 5.5 – 6.5  G. = 4.8 – 5.3. Metallic luster. Color reddish brown to black. Streak light to dark Indian. Red.

Test. infusible. Becomes strongly magnetic on heating in R.F. Slowly soluble in hydrochloric acid; solution with potassium ferrocyanide gives dark blue precipitate (test for ferric iron). Told chiefly by its characteristic Indican – red streak.

Varieties. Specular Hematite. Black hematite with brilliant splendent luster (whence name, specular, mirrolike), in crystals or in foliated masses with micaceous structure.

Columnar to Reniform Hematite, Kidney Ore. Brownish black color, in columnar to reniform shapes with radiating structure, having fibrous appearance (A, pl. III).

Oolitic and Fossil Ore. Impure hematite in small globular or lenticular concretions. At times with fossils.

Earthy Hematite. In pulverulent, earthy form of various shades of reddish brown. Often somewhat hydrated and passing into limonite.

Occurrence. Hematite is a widely distributed mineral in rocks of all ages and forms the most abundant ore of iron. It may occur as a sublimation product in connection with volcanic activities. Occurs as an accessory mineral in feldspathic origin. Found from microscopic scales to enormous masses in connection with metamorphic rocks where it may have originated by the alteration of limonite, siderite, magnetite, etc. Like limonite, it may be formed in irregular masses and beds as the result of the weathering of iron-bearing rocks. The oolitic ores are of sedimentary origin and may occur in beds of considerable size. It is found in red sandstones as the cementing material that binds the quartz grains together.

The crystallized variety is found at many places, more particularly from the island of Elba; St. Gothard, Switzerland, in “iron roses”; in the lavas of V Vesuvius; at Cleator Moor, Cumberland, etc. In the United States the columnar and earthly varieties are found in enormous beds that furnish a large proportion of the iron ore of the world. The chief districts, which are spoken of as iron-ore ranges, are, from east to west, the Marquette; the Penokee-Gogebic Range in northern Wisconsin; the Mesabi Range, north of these different ranges varies from the hard black micaceous specular variety to the soft red earthy type. All of the ore bodies lie in rock troughs witch furnish impervious underlying basements to the deposits. In all of the districts, except the Mesabi, these underlying rocks are in the nature of altered igneous dikes, known as soapstone dikes. The ore bodies lie in more or less broken quartz material, frequently colored red by inclusions o f hematite and called jasper. The origin of these deposits is attributed to the slow concentration of the iron content of a siliceous carbonate rock by downward moving waters. These waters were at last collected in the impervious rock troughs and there deposited their iron content by a replacement of the quartz of the overlying rock. The ores are mined in part by underground methods, and in part, where the ore is soft and lies sufficiently near the surface, by the use of steam shovels. Hematite is also found in the United States in various places in connection with the outcrop of rocks of the Clinton information, from central New York south along the line of the Appalachian Mountains to central Alabama. The most important deposit of the series lie in eastern Tennessee and northern Alabama, near Birmingham. Has been found at Iron Mountain and Pilot Knob is southeastern Missouri. Deposits of considerable importance are located in Wyoming, in Laramie and Carbon counties.

Name. Derived from a Greek word meaning blood, in allusion to the color of the powdered mineral.

Use. Most important ore of iron. In red pigments. As polishing powder, etc.