What are the 7 types of Crystals

7-types of crystals: 

On the basis of axial length in x,y, z-direction, and interfacial angles between them,unit cell can be classified into seven types which are called Seven Crystal System.

7- Crystal Habits
Axial Length
Interfacial Angles
Cubic
a = b = c        
α = β = γ = 90˚
Tetragonal
a = b c        
α = β = γ =90˚
Orthorhombic(Rhombic)
a ≠ b ≠ c        
α = β = γ =90˚
Monoclinic
a ≠ b ≠ c        
α = γ =90˚ ,  β 90˚
Triclinic
a ≠ b ≠ c        
α β γ 90˚
Hexagonal
a = b ≠ c        
α = β = 90 ˚ , γ =120˚
Rhombohedral
a = b = c        
α = β = γ 90˚

Where a,b,c is the length of x,y and z-axis respectively.

α,β,γ  is the interfacial angle between x-axis and y-axis, y-axis and z-axis, z-axis and x-axis respectively.

Note:

Most symmetric crystal -Cubic Crystal
Most unsymmetric crystal -Triclinic Crystal
To remember this crystal system we have derived a formula and i.e. 
            CUTE OUR MOTHER
CU-Cubic
TE-tetragonal
OUR-Orthorhombic
MO-Monoclinic
T-Triclinic
HE-Hexagonal
R-Rhombohedral

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