Since when has any group of humans ever needed a crystal or anything else to rape and pillage? That is mankind's favorite
activity. Having said that ... this is a beautiful crystal. Allison
From: Victor Healey <vic.healey@gmail.com>
To: geology2@yahoogroups.com
Sent: Wednesday, April 17, 2013 7:29 AM
Subject: [Geology2] Did-magical-little-crystal-help-Vikings-rape-pillage-world?
Sunstone (wait for two images to load)
Description Iceland spar, perhaps the medieval sunstone
From Wkipedia…
Research in 2011 by Ropers et al., confirms that one can identify the direction of the sun to within a few degrees in both cloudy and twilight conditions using the sunstone and the naked eye. The process involves moving the stone across the visual field to reveal a yellow entoptic pattern on the fovea of the eye. Alternatively a dot can be placed on top of crystal so that when you look at it from below, two dots appear, because the light is "depolarised" and fractured along different axes. The crystal can then be rotated until the two points have the same luminosity. The angle of the top face now gives the direction of the sun.
The recovery of an Iceland spar sunstone from the Elizabethan ship near Alderney (which sank in 1592) suggests the possibility that the navigational technology may have persisted after the invention of the magnetic compass. Although the stone was found near a navigational instrument, its use remains uncertain.
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