How do scientists check which kind of unit cell is present in a crystal? There are many types of unit cells like:


Tetragonal        Monoclinic      Orthorhombic        Rhombohedral
Hexagonal         Triclinic       Cubic    


But how do scientists identify the type when a sample of the compound is given to them?
X-ray diffraction. Usually computer will tell you automatically nowadays but in the old days you had to check whether the values you got for the miller planes were possible with the symmetry of different unit cells. They discarded the ones that didnt match until the would find the one unit cell which matched the miller planes from XRD