Dear All,
I would be glad to have your suggestion regarding identification and
significance of a mineral which occurs in close association with spinel and
magnetite, the latter are part of a spinel-anorthite symplectite assemblage
formed after garnet and sillimanite. The mineral in question is pleochroic
from reddish brown to light brown, anisotropic, shows straight extinction
and occurs as small blebs around magnetite (granular exsolution?), locally
against green spinel (XMg=0.33). It has a chemical composition of FeO
(26.17), MgO (5.81), Al2O3 (58.73), TiO2 (6.12), ZnO (0.72), Cr2O3 (0.45).
In certain association, Zn may reach upto 4 wt%. The relevant textural
features are shown in an attached file (SKB(E).doc). The top right photo is
a back scatter image of the top left microphotograph. From other textural
data, it appears that there is two stage exsolution from an original Splss
phase, formed after breakdown of grt--(1) an early, relatively magnesian
spl and magnetitess with moderate Usp and Hc components. (2) second stage
exsoln of the unidentified phase from magnetitess phase. Can the phase be
hogbomite? I shall be greatly benefited from your valuable suggestion
regarding its petrologic significance.
With best regards,
Dr. Santanu Kumar Bhowmik
Assistant Professor
Dept of Geology & Geophysics
Indian Institute of Technology
Kharagpur-721 302
E-Mail: [log in to unmask]
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