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The
crystal in the center of this image comprises lamellar
intergrowths (note the stripes) of wide-chain silicates,
or pyriboles, known as "chesterite" and "jimthompsonite." In
contrast to pyroxenes (single-chain) and amphiboles (double-chain),
such pyriboles consist of 3, 4, 5 ... chains linked together.
This sample (ID6-4C) is from a calc-silicate formation
in the 3.8 Ga Isua Supracrustal Belt, West Greenland. Click
on image for enlargement.
(Photo by Prof.
Bob Dymek) |
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