Question

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

• A. All three axial angles are not equal to ${90}^o$
• B. All the three axial angles are equal to ${90}^o$
• C. All the three axial lengths are equal
• D. All the three axial angles and axial lengths are equal

Answer 1

Answer: (A), (C), (D)

All the three axial angles and axial lengths are equal

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 $HgS$ (cinnabar) are example of trigonal crystals.