# Miller Index

Miller index calculations.A) Calcopyrite has axial lengths of a =5.25 A and c = 10.32 A.

1. What is the miller index of the face that cuts a1 and a2 at 10.5 A and does not cut c ?

2. What is the miller index of a face that a1 and a2 at 15.75 A and c at 5.16 A ?

3. What is the formula of Calcopyrite?

4. To what crystal system does it belong ?

B) Barite is orthorhombic and has axial lengths of a=8.87 A, b = 5.45 A and c = 7.14 A.

1. What is the miller index of a face that cuts a at 8.87 A, b at 10.90 A and negative c at 14.28 A ?

2. What is the miller index of a face that cuts a at 17.74 A, b at 10.90 A and does not cut c ?

3. What is the axial ratio of Barite ?

Answers

1. (h,k,l) = (10.5/a1, 10.5/a2, 0) = (2,2,0) = (1,1,0)

2. (h,k,l) = (15.75/a1, 15.75/a2, 5.16/c) = (3,3,0.5) =(6,6,1)

3. the chemical formula is CuFeS2

3. The system is tetragonal scalenohedral class or simply tetragonal

B) The unit cell is a cube having x axis a =8.87, y axis b =5.45 and z axis c =7.14

1. (h,k,l) = (8.87/a, 10.90/b, -14.28/c) = (1, 2, -2)

2. (h,k,l) = (17.74/a, 10.90/b, 0) =(2,2, 0) =(1,1,0)

3. axial ratio of Barite is

8.87 to 5.45 to 7.14 = 1.6289 to 1 to 1.3122