It is a term given to the phenomenon which is exhibited on all non-opaque minerals, leaving amorphous ones and those that crystallize in the isometric system. When a ray of light enters the crystal, it splits up into two separate rays and makes everything observed through the crystal appear as double. In many minerals it is very weak and is observed only through special instruments but in some minerals like Iceland Spar variety of Calcite is strongly visible. Double refraction differs from mineral to mineral. This property is used in identifying gems. It is measured with a refractometer.
Phenomenon exhibited on all non-opaque minerals except for amorphous ones and ones that crystallize in the isometric system. A light ray enters the crystal and splits up into two separate rays, making anything observed through the crystal appear as double. The double refraction on most minerals is so weak that it cannot be observed without special instruments. However, in some minerals, such as the Iceland Spar variety of Calcite it is strongly seen. The double refraction is different in every mineral, and thus can be used to identify gems. Double refraction is measured with a refractometer
splitting a ray into two parallel rays polarized perpendicularly
The ability of a transparent gem mineral to break light into two separate rays as it travels through the stone.
The phenomenon in which each ray of light is split in tow as it enters a noncubic mineral. Each ray travels at different speeds and has its own refractive index.
The ability of most gems to split rays of light into two rays.
In polarized and DIC optical microscopy, double refraction (or birefringence) is defined as the splitting of light into distinct orthogonal ordinary and extraordinary wavefronts in a birefringent material (such as an anisotropic specimen or a Wollaston prism). When a birefringent calcite crystal is placed onto a page of printed words, the effects of double refraction are clearly observed as an overlapping, double image of the text.
Although diamond is normally singly refractive, many gemstones are doubly refractive (bi-refringent), and diamonds can also be doubly refractive because of internal strain or inclusions.
optical effect seeing two images through it Iceland Spar
Phenomenon in which each ray of light is split in two as it enters a non-cubic mineral.
Nearly synonymous with birefringence but may be applied in a restricted sense to transparent (at visible frequencies) media with sufficient birefringence that images seen through them are split. The term originates from the Danish physician Erasmus Bartholinus, who in 1669 wrote about what he observed through the crystalline solid calcite: "objects which are looked at through the crystal do not show, as in the case of other transparent bodies, a single refracted image, but they appear double."
