Form

Crystal system and habit

The habit (from the Latin: habitus, external form) of a crystal is determined by the seven crystal systems to which it belongs (see [BRA 66]).

The occurrence frequency of each system in nature is given in Table 1.1.

Monoclinic

29

Orthorhombic

21

Cubic

15

Triclinic

11

Trigonal

10

Hexagonal

7

Quadratic

4

Total

100

Table 1.1. Bravais' crystalline systems

Metals typically crystallize in an isotropic system (that is, the cubic system).

As far as filtration or drying is concerned, crystals can occur in one of the following forms:

  • - tablet;
  • - prism;
  • - acicular (fibers, needles, rods);
  • - pyramid;
  • - rhombohedron;
  • - tetrahedron;
  • - hexahedron (cubes);
  • - octahedron;
  • - dodecahedron;
  • - scale and plate.

Table 1.2 gives the occurrence frequency of these polyhedra according to the system to which the crystal belongs.

The total for each column is equal to 100.

Attrition is often active in crystallizers. Crystal tops and edges are dulled and their form can approach that of river pebbles.

Monoclinic

Orthorhombic

Cubic

Triclinic

Trigonal

Hexagonal

Quadratic

Tablet

42

31

43

30

37

32

Prism

36

46

29

26

42

29

Acicular

15

19

12

15

11

Pyramids

4

5

10

24

Rhombohedron

9

29

Tetrahedron

10

Hexahedron

31

Octahedron

38

Dodecahedron

21

Scale

7

2

15

Table 1.2. Practical shapes of crystalline systems

 
Source
< Prev   CONTENTS   Source   Next >