Question

Which of the following statement(s) is/are correct regarding trigonal crystal system?

• A. It is also called as rhombohedral crystal system.
• B. All the edge lengths or axial lengths are equal.
• C. All three axial angles are equal but they are not equal to ${90}^o$
• D. All of the above.

Answer 1

The correct option is D All of the above.

Trigonal crystal system is also called as rhombohedral crystal system. For trigonal crystal systems all the edge length or axial length are equal.
$a=b=c$
All three axial angles are equal but they are not equal to ${90}^o$
$\alpha =\beta =\gamma \ne {90}^o$

Calcite ($CaC{O}_3$) and cinnabar $\left(HgS\right)$ are examples of trigonal crystals.