The effect of composition, temperature and pressure on the stability of the 1Tc and 2M polytypes of sapphirine

Christy, AG (1989) The effect of composition, temperature and pressure on the stability of the 1Tc and 2M polytypes of sapphirine. Contributions to Mineralogy and Petrology, 103 2: 203-215. doi:10.1007/BF00378506


Author Christy, AG
Title The effect of composition, temperature and pressure on the stability of the 1Tc and 2M polytypes of sapphirine
Journal name Contributions to Mineralogy and Petrology   Check publisher's open access policy
ISSN 0010-7999
Publication date 1989-01-01
Sub-type Article (original research)
DOI 10.1007/BF00378506
Open Access Status
Volume 103
Issue 2
Start page 203
End page 215
Total pages 13
Publisher Springer-Verlag
Language eng
Subject 1908 Geophysics
1906 Geochemistry and Petrology
Abstract Microprobe analyses and structural characterisation by means of transmission electron microscopy and powder X-ray diffraction are presented for a suite of natural and synthetic sapphirines. Most sapphirines appear to consist of intergrowths of the common 2M polytype with minor amounts of the 1Tc phase, although the converse situation is found in some cases. Attempts to correlate the structural state of the mineral with other factors reveal that: (i) There is no strong relationship between mean tetrahedral cation radius or mean octahedral cation radius and the preferred polytype. The Tschermak substitution M2+M4+-M3+M3+ does not appreciably influence the 1Tc-2M equilibrium, (ii) However, the total content and mean oxidation state of iron in sapphirine are important in this respect. Fe2+ stabilises the 2M phase, whereas Fe3+ stabilises the 1Tc phase. (iii) P-T estimates for the host rocks, and estimates for the conditions of sapphirine crystallisation, where obtainable, suggest that the 1Tc phase is stable at lower T and higher P than the 2M phase. Some quantitative constraints are inferred.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
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