A dichroscope is a pocket instrument used in the field of

gemology Gemology or gemmology is the science dealing with natural and artificial gemstone materials. It is a geoscience and a branch of mineralogy. Some jewelers (and many non-jewelers) are academically trained gemologists and are qualified to identif ...

, and can be used to test transparent

gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...

s (crystals). Experienced gemologists, observing the

pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgrou ...

of some gems, can successfully detect gemstones from other artificial stones using this instrument. There are two types of dichroscopes available: calcite and polarizing. Of the two, calcite gives better results and is widely used by experienced gemologists. With the polarizing type, only one pleochroic color can be seen at a time. This makes the process time-consuming and difficult, though it is the most economical way to get results. The dichroscope has been used since at least the start of the nineteenth century.

Calcite Dichroscope

A calcite dichroscope shows a gem's pleochroic colors in contrast with one another, allowing the viewer to easily determine whether the stone is singly or doubly refractive (uniaxial or biaxial, respectively). Singly refractive stones do not split light that enters them, leaving light as a single beam as it exits the stone. On the contrary, doubly refractive stones may split an entering light beam into two rays (an ordinary ray and an extraordinary ray) depending on the angle, a property known as

birefringence Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefring ...

. Calcite dichroscopes are effective because the inner

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

component is able to split the entering light beam coming through the stone, revealing whether the stone is isotropic, uniaxial or biaxial.

References

Gemology Scientific instruments {{geology-stub