[mass noun] A transparent variety of calcite, showing strong double refraction.
- ‘Nodules filled with clear double-refractive Iceland spar with celadonite inclusions have also been found here.’
- ‘The large, transparent crystals known as Iceland spar, however, are pure calcite.’
- ‘Certain crystals will split incoming light into two separate rays; Iceland spar is one such crystal, as are calcite and quartz.’
- ‘He cited as an example Huygens's hypothesis that the extraordinary ray in doubly-refracting Iceland spar is propagated elliptically.’
- ‘He spent two years there, in particular studying the double refraction Bartholin had discovered in Iceland spar crystal.’