Electron diffraction patterns have been taken from a large variety of natural single crystals of α-Fe 2 O 3 (haematite) which had previously been heated to 500°C. Some of these showed additional patterns similar to those observed by Finch and Sinha in 1957. Measurements of the basic plane spacings associated with the extra patterns showed that these differed considerably from the corresponding basic plane spacings of α-Fe 2 O 3 . This result is in contradiction to the findings of Finch and Sinha who claimed that the basic plane spacings associated with the extra patterns approximated closely to those of α-Fe 2 O 3 . There is therefore no justification for assuming that a new form of Fe 2 O 3 (β-Fe 2 O 3 ) exists. Experiments were also carried out on crystals of α-Fe 2 O 3 which had been heated to temperatures between 700° and 1000°C. In some cases oriented layers of Fe 3 O 4 (magnetite) were observed but no evidence was found for the presence of γ-Fe 2 O 3 (maghemite) in contrast to the results of Finch and Sinha These investigators claimed that γ-Fe 2 O 3 was formed when α-Fe 2 O 3 crystals were heated in air to temperatures above 700 C.
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Blackman et al. (1960) studied this question.
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