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Surinamite: A high-temperature metamorphic beryllosilicate from Lewisian sapphirine-bearing kyanite-orthopyroxene-quartz-potassium feldspar gneiss at South Harris, N.W. Scotland by Sotaro Baba; Edward S. Grew; Charles K. Shearer; John W. Sheraton is a Earth and Planetary Sciences article available to read on EtoBox.

What is Surinamite: A high-temperature metamorphic beryllosilicate from Lewisian sapphirine-bearing kyanite-orthopyroxene-quartz-potassium feldspar gneiss at South Harris, N.W. Scotland about?

The sapphirine-like mineral surinamite, (Mg,Fe 2+ ) 3 (Al,Fe 3+ ) 3 O[AlBeSi 3 O 15 ], occurs at South Harris as tiny grains enclosed in kyanite or as tabular grains up to 1 mm long mostly surrounded by Si-rich cordierite. A few surinamite grains enclose orthopyroxene, sillimanite, and Si-rich sapphirine. Ion microprobe analyses gave 3.52 to 3.81 wt% BeO (0.766 to 0.824 Be atoms per formula unit) and 2 to 13 ppm B in surinamite. Excess Si suggests the presence of significant BeO in cordierite and sapphirine. Given the anti-clockwise P-T-time path inferred for the South Harris rock, we suggest that surinamite formed at first by the continuous reaction BeSiAl -2 (in sapphirine) + sillimanite + orthopyroxene → surinamite + quartz and, subsequently, by the discontinuous reaction Be-depleted sapphirine + quartz → surinamite + orthopyroxene + kyanite with increase of P to >12 kbar at 850-900 °C. Surinamite reacted with orthopyroxene, kyanite, and quartz to form beryllian cordierite during subsequent decrease in P and T. The high-silica content and peraluminous composition of the surinamite-bearing gneiss are consistent with a metasedimentary origin; this rock is markedly depleted in Th (

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Author

Sotaro Baba; Edward S. Grew; Charles K. Shearer; John W. Sheraton

Publisher

Mineralogical Society of America

Published

2000

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)