Fibrous hematites

Retrograde metamorphic processes, linked to hydrothermal fluid circulation, finally produced a new mineral assemblage constituted mainly by tremolite-actinolite> epidote + chlorite + quartz + sericite + titanite + hematite. The amphibole appears as green fibrous crystals over clinopyroxene and other anhydrous minerals. 

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. 

Fig. 34. Relict organic structures in Precambrian cherty iron-formations (after La Berge). I = type A structure, well preserved due to carbonaceous matter in chert matrix note fibrous surface and clear interior (lower chert unit of Biwabik Iron Formation, Pilotac mine, Minnesota) 2 = type A structure, largely replaced by greenalite 3 = type A structure, preserved due to unidentified brown substance (hematite ) in chert matrix (Belcher Islands iron-formation) 4 = type B structure (Eosphaera tyleri), well preserved due to carbonaceous matter in chert matrix (Gunflint district) 5 = type B structure in which most of the organic matter has been replaced by extremely fine hematite (Vicar mine, Gogebic district) ...

Uptake ean similarly be increased by exogenous sources of AOS. Brief exposure to whole cigarette smoke, which is a highly concentrated source of AOS and other radicals, and then to a mineral dust suspension produces considerably greater uptake of asbestos, titanium dioxide, fibrous silicon carbide, and talc (51 -53 Fig. 2). The increase in uptake is proportional to the dose of cigarette smoke, and the smoke effect can be inhibited by catalase, superoxide dismutase (which destroys superoxide anion), or deferoxamine (see Fig. 2). The effects of low levels of ozone are similar (Fig. 3), but differ from cigarette smoke in that superoxide dismutase is not protective (126). Smoke also fails to enhance the uptake of nonfibrous silicon carbide or iron oxide (hematite 53) the latter observation is particnlarly interesting because it was recently shown (127) that hematite does not catalyze the formation of AOS. This observation emphasizes the idea that redox-active surface iron, as opposed to compositional iron, is cracial to AOS formation and particle nptake. 

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