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In 1669, Rasmus Bartholin made an observation of double refraction in a calcite crystal and documented it in a published work in 1670. [2] Later, in 1690, Huygens identified polarization as a characteristic of light and provided a demonstration using two identical blocks of calcite placed in succession.
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO 3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed ...
A calcite crystal laid upon a graph paper with blue lines showing the double refraction In this example, optic axis along the surface is shown perpendicular to plane of incidence.
Crystals may have a single optic axis, in which case they are uniaxial, or two different optic axes, in which case they are biaxial. Non-crystalline materials generally have no birefringence and thus, no optic axis. A uniaxial crystal (e.g. calcite, quartz) is isotropic within the plane orthogonal to the optic axis of the crystal.
However, if the crystal has a higher symmetry, a smaller angular range such as 90° or 45° may be recorded. The rotation axis should be changed at least once, to avoid developing a "blind spot" in reciprocal space close to the rotation axis. It is customary to rock the crystal slightly (by 0.5–2°) to catch a broader region of reciprocal space.
Iceland spar, formerly called Iceland crystal (Icelandic: silfurberg [ˈsɪlvʏrˌpɛrk], lit. ' silver-rock ' ) and also called optical calcite , is a transparent variety of calcite , or crystallized calcium carbonate , originally brought from Iceland , and used in demonstrating the polarization of light .
Optical properties of common minerals Name Crystal system Indicatrix Optical sign Birefringence Color in plain polars Anorthite: Triclinic: Biaxial (-) 0.013
The density, or specific gravity, is 2.7 cm³/g. The hardness is three by the Moh’s scale of hardness. Formed in the way similar to stalagmites and stalactites with water dripping, there are many crystal formations of calcite. It can be in the crystal system of trigonal in the class of hexagonal scalenohedral.