Question

question 19 (2 points) an hexagonal crystal with a c > a is uniaxial optically positive biaxial a and b mystical

Explanation:

Hexagonal crystals with c > a are uniaxial. Uniaxial crystals have one optic axis, while biaxial crystals have two. The terms "optically positive" describe a property related to the refractive - index ellipsoid and is not relevant to identifying the crystal based on its hexagonal structure with c > a. "Mystical" and "a and b" are not relevant to the crystal - axis classification here.

Answer:

uniaxial