Question

Which one of the following minerals has crystallographic axes \( a_1 = a_2 \neq c \) and all interaxial angles equal to 90°?

• A. Beryl
• B. Barite
• C. Plagioclase
• D. Zircon

Hint:

Understanding crystal systems and their symmetry is essential for identifying minerals based on their crystallographic axes and angles.

Answer 1

The Correct Option is D

The crystallographic structure described in the question corresponds to a tetragonal system, where:
\( a_1 = a_2 \neq c \)
All interaxial angles are 90°.
Among the listed minerals:
Beryl: Has an hexagonal crystal system.
Barite: Has an orthorhombic system, not tetragonal.
Plagioclase: Belongs to the triclinic system.
Zircon: Has a tetragonal crystal system with \( a_1 = a_2 \neq c \) and interaxial angles of 90°.
Step 2: Conclusion
Option (D) Zircon is the correct answer, as it fits the conditions of the tetragonal system described.