Quartz has hexagonal 32 point group symmetry. Its unit cell dimensions are a = 4.914 Å and c = 5.405 Å. It is uniaxial a

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Quartz has hexagonal 32 point group symmetry. Its unit cell
dimensions are a = 4.914 Å and c = 5.405 Å. It is uniaxial and
optically positive. The refractive indices of the slow and fast
rays are 1.553 and 1.544, respectively.
What is the angle, α, between the ordinary and extraordinary
rays?
tan(α + θ) =
[nω2/nε2].[cos(90-θ)/sin(90-θ)]