Hematite micaceous

Fig. 4.19 Upper Crystal forms of platy and rhombohedral hematite (Courtesy H. Stanjek). Lower Micaceous hematite from Western Australia (Courtesy R. Giovanoli, magnification 250x).

Micaceous iron oxides are produced in a process which involves heating FeCl3 and iron at 500-1000 °C to form molten Fe complexes which are then oxidized to micaceous hematite the diameter of the plates can be varied from 5 to 75 pm depending on whether the oxide is intended for use in a primer paint or a topcoat (Carter, 1988). 

Hydrothermal conversion of either ferrihydrite or goethite at 250-300 °C in alkaline media for some hours, followed by a further stage of growth at higher pH (Os-tertag, 1994). Micaceous plates of hematite result. 

This same oxide exists in a variety of other forms, such os a fibrous mass, with the fibres radiating from a centre, in which state it is termed the red hematite or fibrous iron ore. When the ore is an amorphous mass, it is termed compact iron, ore when mixed with clay and other earthy matters, red ochre when hard, and combined with silica, jaspery ore / whon in scales of a black metallic lustra, it is known as micaceous iron ore or iron glance. 

Hematite is found in large quantities in the vicinity of Malaga in Spain (Spanish red) and near the Persian Gulf (Persian red). The Spanish reds have a brown undertone. Their water-soluble salt content is very low and their Fe203 content often exceeds 90 %. The Persian reds have a pure hue, but their water-soluble salt content is disadvantageous for some applications. Other natural hematite deposits are of only local importance. A special variety occurs in the form of platelets and is extracted in large quantities in Karnten (Austria). This micaceous iron oxide, is mainly used in corrosion protection coatings. 

Micaceous iron oxide [1317-60-8] Fe203 (specular hematite) 4.6-48 dark gray... 

Micaceous iron oxide consists of pure or doped hematite (a-Fe203). Its density is 4.6-4.8 g cm . Micaceous iron oxide can also be obtained by hydrothermal synthesis in alkaline media. However, the duU dark color is as unappealing as that of the natural product If substantial amounts of dopants are incorporated, the aspect ratio can be increased up to 100, resulting in a much increased luster. The color can be also shifted to a more attractive reddish brown so that the products can be used for decorative purposes [5.126, 5.133]. 

Prato has described the results of geological investigations in the area. Tabular, lens-shaped bodies occur in apatite-rich quartz mica schists composed of alternating muscovite and quartz + feldspar beds interbedded with the acid metavolcanics petrochemical analyses of the host rocks indicate a composition intermediate between feldspathic sandstones and argillites. The mineral association is pitchblende + pyrite-I-chalcopyrite + tetrahedrite -I- hematite, the first two being the most abundant. The uranium -I- sulphide mineralization is parallel both to the schistosity and to the younger tectonic deformations produced by the Alpine dynamo-metamorphism in particular, pitchblende is confined to the apatite-rich micaceous beds. Apatite is clearly replaced by pitchblende. 

---