Original paper

Growth defects of a melanite crystal

Agrosí, Giovanna; Scandale, Eugenio; Digennaro, Maria Arcangela

Neues Jahrbuch für Mineralogie - Abhandlungen Band 176 Heft 1 (2001), p. 89 - 107

33 references

published: Feb 26, 2001

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ArtNo. ESP154017601005, Price: 29.00 €

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Abstract

A melanite crystal from the volcanic complex of Colli Albani (Italy) was studied by means of Optical Microscope (OM), X-ray Diffraction Topography (XRDT) and Electron Microprobe Analysis (EMPA). Extended defects - dislocations, inclusions, precipitates and growth sector boundaries - were observed, allowing the crystal growth history to be reconstructed and three successive growth stages to be determined. The chemical zonings of the sample, investigated by means of EMPA, were related to the morphological evolution vs. time, obtained by XRDT, and this allowed the discrimination between concentric and sector zonings to be made. Concentric zoning concerned continuous smooth concentration variations of Si02, Al2O3 and TiO2. Sector zoning occurred sharply in crossing the boundaries between n {211} and d {110} growth sectors where TiO2 concentrations resulted higher in the {211} growth sectors with respect to {110} whereas Al2O3 resulted lower.

Keywords

Melanitegrowth defectsmorphological evolution vs. timeconcentric zoning and sector zoning