Free Republic

Physicists from Eötvös Loránd University in Hungary have determined that the sunstones claimed to be used by Vikings to navigate on foggy and cloudy days could provide accurate results. Vikings living between 900 and 1200AD did not have magnetic compasses, and their ability to navigate was attributed in part to the use of calcite, cordierite or tourmaline crystals which functioned as linear polarizers to help them determine geographic north. The crystals can split sunlight into two beams, and when the crystal is turned, splitting the two beams at the same brightness, a navigator could see the polarized rings around the...

I've been meaning to do this for a long time. Below is a fine specimen of banded tourmaline. Tourmalines like this are generated in pegmatites; see diagram below the picture, with description and link to more information. (The diagram is not from the same place as the description.) The Pegmatite Zone, from whence cometh this text: "A pegmatite is a coarse grained igneous rock (formed deep within the earth) having a grain size of 3cm or more. Mostly pegmatites are granitic in origin, that is they are composed of granite and its constituents like quartz, feldspar and mica. In addition...