Form and stuff

Question 1

Symmetry Operations

Answer 1

A transposition of an object

Includes 3 types:

1. rotations
2. inversions
3. translations

There are 10 permissible rotations

1. proper - 1, 2, 3, 4, 6
2. improper - i, -2 = m, -3, -4, -6

Question 2

Point Groups

Answer 2

There are 32 possible combinations of rotational symmetry operations that each correspond to one of the 7 crystal systems

Question 3

Morphology

Answer 3

The morphology of a perfect crystal, in general, reflects the maximum symmetry that a crystal can have.

Question 4

Crystal Form

Answer 4

A crystal fce plus its symmetric equivalents

Question 5

Special Form

Answer 5

A crystal form that is repeated by symmetry operations onto itself so that there are fewer faces as the order of the group.

Question 6

General Form

Answer 6

A form that is not repeated onto itself by the symmetry operations so that it has the same number of faces as the order of the group

Question 7

Closed Form

Answer 7

Encloses a volume

ex: cube, tetrahedron, octahedron

Question 8

Open Form

Answer 8

Does not enclose a volume

ex: prism, pinnacoid

Question 9

Miller Indices

Answer 9

A plane of a crystal cuts crystallographic axes at intercepts

May be a cleavage plane, a crystal face, or any diffracting X-ray plane

Always in relation to the crystallographic axes, not any orthogonal system of convenience

General form is (h k l)

Question 10

32 Crystal Classes

Answer 10

There are 32 point groups - combinations of proper and improper rotations

Each corresponds to one of the 32 crystal classes

Each is assigned to one of the seven crystal systems

Question 11

Order

Answer 11

The order of the group is the number of operations of the group