2- 3D Crystal System

Question 1

UNIT CELL

Answer 1

Ththe smallest indicisible ‘building block’ of a structure

Question 2

7 Crystal Systems:

Answer 2

CUBIC                          
TETRAGONAL
ORTHORHOMBIC    
MONOCLINIC
TRICLINIC

HEXAGONAL
TRIGONAL

‘Could tell Oregon My Tricky Home Troubles’

Question 3

How to determine a crystal system of an unknown mineral?

Answer 3

1. Consider SHAP and SIZE of the unit cell (determined using X-Ray Diffraction (XRD)
2. Examine the shape and symmetry of the macroscopic crystals which reflect the symmetry of the unit cell

Question 4

CUBIC MINERALS:

Answer 4

x = y = z , a = b = g = 90°

• properties of a cube are the same in all directions

Rotate it round and not be able to determine the three axis
THEREFORE the properties of cubic Minerals do not change as you rotate the crystal

Question 5

TETRAGONAL SRYSTAL SYSTEM

Answer 5

x = y /=z , a = b = g = 90°

Question 6

ORTHORHOMBIC

Answer 6

x /= y /= z , a = b = g = 90°

Question 7

MONOCLINIC

Answer 7

x/=y/=z , a/=g/=90°, b= 90°

)pushed over rectangle

Question 8

Triclinic

Answer 8

x /= y/= z , a/=b/=g/= 90°

Question 9

GROUP ONE

Answer 9

Based in THREE Principal Axes

Cubic, Tetragonal, Orthohombic, Monoclinic, Triclinic

Question 10

Hexagonal and Trigonal Crystal Systems

Answer 10

Group 2- based on 4 principal Axes
a1=a2=a3z, g1=g2=g3=120°

(sometimes called Rhombic)

Question 11

PRIMITIVE LATTICE

Answer 11

All the atoms are in the corners (P)

Question 12

BODY CENTERED

Answer 12

put all the atoms at the corners and in the center of the cell (I)

Question 13

BASE CENTRED

Answer 13

Atoms at the corners and in the center of one face - depending on the face, you use wither (A,B or C) - using whichever letter the face is opposite to

Question 14

Face CENTRED

Answer 14

Atoms at the corners and in the centre of ALL faces (F)

Question 15

What about for Group 2 unit cells? type of lattice?

Answer 15

hexagonal and trigonal - use primitive space group ‘R’

Question 16

Which lattice can you not have in a Cubic system?

Answer 16

cant have a ‘C’ lattice (base centred) as anything you do to one face you must so to the other too

Question 17

Lattices possible in Monoclinic crystal Systems

Answer 17

P and C

Question 18

What are the 14 Bravais Lattices

Answer 18

Cubic: P, F, I            Tetragonal: P, I
Orthorhombic: P, C, F, I
Monoclinic: P, C      
 Triclinic: P
Hexagonal: R
Trigonal: R

Question 19

How many Hexagonal: R

permutations can be formed from the different atom identities etc.

Answer 19

230 permutations or ‘SPACE GROUPS’

Question 20

what would C2/m mean?

Answer 20

C lattice
2 fold axis
a mirror plane (m)
(monoclinic- sanadine feldspar)

Question 21

P21 21 2

Answer 21

P lattice

three, 2 fold axes

Question 22

P¬1

Answer 22

P lattice 
no symmetry
(¬1 means rotating 360 degree, there is no symmetry)

Question 23

Glides

Answer 23

a 3D symmetry element where a combination of a translation and a reflection.

Question 24

Types of Glides

Answer 24

a-glide- glide is parallel to the a-axis

d-glide- across a diagonal

n-glide - across the body of the crystal

Question 25

Fd3m

Answer 25

F lattice,
3 fold axis,
d-glide,
a mirror plane,
(cube-diamond)

Question 26

F¬43m

Answer 26

F lattice ,
3 fold axis,
4 fold axis,
and a mirror plane
bar means that the 4-fold axis and the 3 fold axis operate in different directions

Question 27

Symmetry elements used to determine the crystal shape:

Answer 27

fold-axis
mirror planes
centre of invertion (aka centre of symmetry)

Question 28

Requirements for Each Crystal System

MINIMUM SYMMETRY REQUIREMENTS

Answer 28

CUBIC: 4 three-fold axes
TETRAGONAL: 1 four-fold axis
ORTHORHOMBIC: 3 two-fold axes
HEXAGONAL:	1 six-fold axis
TRIGONAL: 1 three-fold axis
MONOCLINIC: 1 two-fold axis
TRICLINIC: no symmetry