12-31-2022, 09:07 PM
Or fragments of the mineral perhaps, as discussed here:
The idea that the Vikings navigated across the Atlantic using birefringent Iceland spar (calcite) to locate the Sun's position on cloudy days is surely one of the most ingenious and captivating recent hypotheses about ancient materials use. The suggestion itself is an old one, but has been given strong support in new experiments by Ropars and colleagues.
A narrow beam of polarized light passing into the mineral is split into two by the optical anisotropy that causes birefringence. The 'ordinary' beam behaves as it would in glass; the 'extraordinary' beam is parallel but displaced from it, defying Snell's law. Light passing through a hole in a screen over a calcite crystal therefore forms two images on the far side. When the crystal is oriented to equalize their brightness, it completely depolarizes the light.
https://www.nature.com/articles/nmat3188
The idea that the Vikings navigated across the Atlantic using birefringent Iceland spar (calcite) to locate the Sun's position on cloudy days is surely one of the most ingenious and captivating recent hypotheses about ancient materials use. The suggestion itself is an old one, but has been given strong support in new experiments by Ropars and colleagues.
A narrow beam of polarized light passing into the mineral is split into two by the optical anisotropy that causes birefringence. The 'ordinary' beam behaves as it would in glass; the 'extraordinary' beam is parallel but displaced from it, defying Snell's law. Light passing through a hole in a screen over a calcite crystal therefore forms two images on the far side. When the crystal is oriented to equalize their brightness, it completely depolarizes the light.
https://www.nature.com/articles/nmat3188