Crystal Systems

Question 1

Isometric

Answer 1

a=b=c
All axes @90 degrees

three 4-fold, four 3-fold

Question 2

Hexagonal

Answer 2

a1=a2=a3
Intersecting @ 120 degrees, c perpendicular to plane

one 6-fold, two 2-fold

Question 3

Tetragonal

Answer 3

a=b not=c
Alpha, Beta, Gamma = 90 degrees

one 4-fold, two 2-fold

Question 4

Orthorhombic

Answer 4

a not=b not=c
Alpha, Beta, Gamma = 90 degrees

three 2-fold

Question 5

Monoclinic

Answer 5

a not=b not=c
Alpha & Gamma = 90 degrees, Beta>90 degrees

one 2-fold

Question 6

Triclinic

Answer 6

a not=b not=c
Alpha, Beta, Gamma not= 90 degrees

No symmetry

Question 7

Alpha

Answer 7

Angle between b and c

Question 8

Beta

Answer 8

Angle between a and c

Question 9

Gamma

Answer 9

Angle between a and b

Question 10

Unit Cell

Answer 10

Smallest unit of a structure, fits integral number of formula units, each corner identical, symmetry expressed at the atomic level.

Question 11

Miller Indices Steps

Answer 11

1) Determine intercepts
2) Take reciprocals
3) Multiply by their common number
4) Clear fractions

Question 12

Pedion

Answer 12

Open

Single face

Question 13

Pinacoid

Answer 13

Open

Two parallel faces

Question 14

Dome

Answer 14

Open

Two non parallel faces with mirror plane between

Question 15

Sphenoid

Answer 15

Open

Two nonparallel faces with two-fold rotation axis

Question 16

Prism

Answer 16

Open

3, 4, 6, 8, 12 faces, all parallel to same axis.

Question 17

Pyramid

Answer 17

Open

3, 4, 6, 8, 12 nonparallel faces that meet at a point.

Question 18

Dipyramid

Answer 18

Closed

6, 8, 12, 16, or 24 faces.

Question 19

Rhombohedron

Answer 19

Closed

Six faces, three at top alternate with three at bottom. Two faces offset by 60 degrees.