Question

Crystals can be classified into....... basic crystal systems.

• A. 7
• B. 4
• C. 14
• D. 3

Answer 1

The correct option is A 7

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.
Almost all the crystals found in nature, conform to one of the seven crystal systems.
The seven crystal systems are

Crystal sysytem	Edge lengths	Angles
Cubic	$a=b=c$	$\alpha =\beta =\gamma ={90}^o$
Tetragonal	$a=b\ne c$	$\alpha =\beta =\gamma ={90}^o$
Orthorombic	$a\ne b\ne c$	$\alpha =\beta =\gamma ={90}^o$
Hexagonal	$a=b\ne c$	$\alpha =\beta ={90}^o;\gamma ={120}^o$
Rhombohedral	$a=b=c$	$\alpha =\beta =\gamma \ne {90}^o$
Monoclinic	$a\ne b\ne c$	$\alpha =\gamma ={90}^o;\beta \ne {90}^o$
Triclinic	$a\ne b\ne c$	$\alpha \ne \beta \ne \gamma \ne {90}^o$