Goethite Composition, Crystallization & Structure

Composition. FeO(OH) or Fe₂O₃.H₂O = Oxygen 26,. Iron 62.9, water 10.1.

Crystallization. Orthorhombic. Prismatic, vertically striated. Often flattened parallel to brachypinacoid. In acicular crystals at times.

Structure. Massive, reniform, stalactitic, with radiating fibrous structure. Foliated. Rarely in distinct crystals.

Physical Properties. Perfect cleavage parallel to brachypinacoid. H. = 5-5.5. G. = 4.37. Adamantine to dull luster. Silky luster in certain fine scaly or fibrous varieties. Color yellowish brown to dark brown. Streak yellowish brown (same as for limonite)).

Test. difficulty fusible 85-5.5). Becomes magnetic in R.F. Water in c.T. Told chiefly by the color of its streak and distinguished from limonite by its tendency to crystallize and the small amount of water which it contains.

Occurrence. Occur with the other oxides of iron, hematite and limonite. Also found in quartz as an alteration product of a sulphide. Found at Eiserfeld in Westphalia; from Pribam, Bohemia; at Lostwithiel, Cornwall. In the United States in connection with the Lake Superior hematite deposits, particularly at Negaunee, Michigan. In Colorado from Florissant, Teller Co., and in the Pike’s Peak region.

Use. A minor ore of iron.

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