CRYSTALLOGRAPHYCRYSTALLOGRAPHY

TRIVIATRIVIA

FINAL ROUND!FINAL ROUND!

Round 3 – Question 1Round 3 – Question 1

Twins are said to add another level of symmetry to a crystal. Why is this?

Round 3 – Question 2Round 3 – Question 2

Which of the following statements Which of the following statements about twins are true?about twins are true?

- penetration twins form by reflective penetration twins form by reflective symmetry across a mirror planesymmetry across a mirror plane

- the composition plane of contact the composition plane of contact twins corresponds to a mirror planetwins corresponds to a mirror plane

- polysynthetic twins form from polysynthetic twins form from variably oriented mirror planesvariably oriented mirror planes

Round 3 – Question 3Round 3 – Question 3

The smallest unit of lattice points that define the basic ordering of atoms in a mineral is called what?

Round 3 – Question 4Round 3 – Question 4Which of these 2-D lattice nets is not primitive?

Round 3 – Question 5Round 3 – Question 5

Besides translation, what other symmetry element is possible in 2D lattices that is not present in point group symmetry of single crystals?

Round 3 – Question 6Round 3 – Question 6

These 3D unit cell types are possible in what crystal class?

Round 3 – Question 7Round 3 – Question 7

Screw axes combine what two symmetry operations?

Round 3 – Question 8Round 3 – Question 8

Which image is an example of a right-handed screw axis?

Round 3 – Question 9Round 3 – Question 9

The space group - P6P633/m2/c2/m /m2/c2/m belongs to what crystal system?

Round 3 – Question 10Round 3 – Question 10

What is the maximum possible number of symmetry combinations that define 3D lattice arrays?

Extra Credit QuestionExtra Credit Question

Choose the number of points you wish Choose the number of points you wish to wagerto wager

What unit cell type and symmetry operations are present in the space group: I41/a2/m2/d and what crystal system does it belong to?

Round 3 – Question 1Round 3 – Question 1

Twins are said to add another level of symmetry to a crystal. Why is this?Twin symmetry Twin symmetry elements do not elements do not usually correspond to usually correspond to crystal symmetry crystal symmetry elementselements

Round 3 – Question 2Round 3 – Question 2

Which of the following statements Which of the following statements about twins are true?about twins are true?

- penetration twins form by reflective penetration twins form by reflective symmetry across a mirror planesymmetry across a mirror plane

- the composition plane of contact the composition plane of contact twins corresponds to a mirror planetwins corresponds to a mirror plane

- polysynthetic twins form from polysynthetic twins form from variably oriented mirror planesvariably oriented mirror planes

Round 3 – Question 3Round 3 – Question 3

The smallest unit of lattice points that define the basic ordering of atoms in a mineral is called what?

A Unit CellA Unit Cell

Round 3 – Question 4Round 3 – Question 4Which of these 2-D lattice nets is not primitive?

Round 3 – Question 5Round 3 – Question 5

Besides translation, what other symmetry element is possible in 2D lattices that is not present in point group symmetry of single crystals?

Glide LinesGlide Lines

Round 3 – Question 6Round 3 – Question 6

These 3D unit cell types are possible in what crystal class?

OrthorhombicOrthorhombic

Round 3 – Question 7Round 3 – Question 7

Screw axes combine what two symmetry operations?

Rotation and TranslationRotation and Translation

Round 3 – Question 8Round 3 – Question 8

Which image is an example of a right-handed screw axis?

Round 3 – Question 9Round 3 – Question 9

The space group - P6P633/m2/c2/m /m2/c2/m belongs to what crystal system?

HexagonalHexagonal

Round 3 – Question 10Round 3 – Question 10

What is the maximum possible number of symmetry combinations that define 3D lattice arrays?

230230

Extra Credit QuestionExtra Credit QuestionWhat unit cell type and symmetry operations are present in the space group: I41/a2/m2/d and what crystal system does it belong to?Unit Cell: Body-centeredUnit Cell: Body-centeredSymmetry Operations:Symmetry Operations:

4-fold screw axis with a perpendicular 4-fold screw axis with a perpendicular glide glide plane with translation in the a plane with translation in the a directiondirection

2-fold rotation axis with a perpendicular 2-fold rotation axis with a perpendicular mirror planemirror plane

2-fold rotation axis with a perpendicular 2-fold rotation axis with a perpendicular diamond glide planediamond glide plane

Crystal System: TetragonalCrystal System: Tetragonal

And the winners are...And the winners are...