Wednesday, 25 May 2011

Iolite ~

Iolite is the gem form of cordierite.  This is a lovely stone of somewhat watery appearance.  The colouration of the beads shown here varies but tends towards indigo. 

Reading the Wikipedia article linked to above I came across this astonishing passage:
It has also been called "water-sapphire" and "Vikings' Compass" because of its usefulness in determining the direction of the sun on overcast days, the Vikings having used it for this purpose[7]. This works by determining the direction of polarization of the sky overhead. Light scattered by air molecules is polarized, and the direction of the polarization is at right angles to a line to the sun, even when the sun's disk itself is obscured by dense fog or lies just below the horizon.[8]

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