Question

Crystal system 'A' has all the edge lengths as same, $a=b=c$. Which of the following(s) is/are the possible crystal system for the given crystal 'A'?

• A. Cubic
• B. Orthorombic
• C. Rhombohedral
• D. Tetragonal

Answer 1

Answer: (A), (C)

Rhombohedral

For 3D-space lattice, there are seven unique and basic unit-cell shapes (primitive unit cells) with varying elements of symmetry in a three-dimensional space.
Out of 7 crystal system, only cubic and rhombohedral has same edge length for all the sides.
Cubic crystal system:
$a=b=c;\alpha =\beta =\gamma ={90}^o$

$NaCl,ZnS$ and $Cu$ are examples of cubic crystals.

Rhombohedral crystal system:
$a=b=c;\alpha =\beta =\gamma \ne {90}^o$

Calcite and $HgS$ are examples of rhombohedral crystals.