Question

Which one of the following is biaxial crystal?
(A) Calcite
(B) Quartz
(C) Tourmaline
(D) Topaz

Answer 1

Hint: It is a crystal of orthorhombic crystal systems. Its chemical composition is mostly silicate. It is also known as the stone of good fortune and devotion.

Complete answer:
-Let us discuss a bit about the biaxial crystals which according to my point of view you should know what the biaxial crystals are. As their name suggests, biaxial crystals have two optical axes around which light is propagated at the same velocity. There are two plane polarised components of every other wave propagation path at right angles to each other and to the propagation direction; both have unequal velocities. A helpful factor related to the optic symbol is the angle between the optic axes.
-All of the minerals in the orthorhombic, monoclinic, or triclinic crystal structures that crystallise are biaxial. There are two optic axes in biaxial crystals, and this separates biaxial from uniaxial crystals. Biaxial crystals have refractive indices, like uniaxial crystals, that differ between two extremes, but have a special intermediate refractive index as well. Topaz is a crystal like that.

The correct option is D.

Note:Topaz is found in jewellery, rings, earrings, necklaces, pendants and bracelets in all various colours. The blue, orange, and pink colours are most often cut as gemstones, and as an affordable diamond simulant, colourless topaz is becoming more and more common.