Question

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

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

Answer 1

Answer: (B), (D)

All three axial angles are not equal to ${90}^o$

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.