Hexagonal crystal system

The hexagonal system has four crystallographic axes consisting of three equal horizontal, or equilateral axes at 120 degrees to each other, as well as one vertical axis which is perpendicular to the other three. This vertical axis can be longer or shorter than the horizontal axes.

The system has the following forms:

Prism
Pinacoid
Dipyramid
Ditrigonal Pyramid
Trigonal Prism
Ditrigonal Prism.

Prisms have a set of faces that run parallel to an axis of a crystal, yet never converge with it. The hexagonal prism is composed of 6 faces which are parallel to a 6-fold rotation axis.

A pinacoid is composed of only two parallel faces. In this case, the top and bottom face are the pinacoid forms.

Blue Beryl crystals exibit both hexagonal prism and pinacoid forms

Side view of beryl

Hexagonal dipyramid: 12-faced form which has a 6-fold axis and comes together in a point. In the image below this would be the top and bottom portion. The vertical faces make up the hexagonal prism, in which all faces in the prism have a 6-fold rotation axis.

This hanksite specimen shows both hexagonal prism and dipyramid forms

Apatite belongs to the hexagonal system, both prism and dipyramid forms

Apatite side view, hexagonal shape is very evident

Side view of apatite

Quartz shows both prism and dipyramid hexagonal crystal forms

Ditrogonal pyramid: In a ditrigonal pyramid there are six faces about a 3-fold rotation axis. These faces come together and meet in a point.

Dravite: hexagonal system, ditrigonal pyramid

Dravite with added lines to highlight the axes

Dravite: hexagonal system, ditrigonal pyramid

Trigonal prism: A trigonal prism has three faces parallel to each other about a 3-fold rotation axis

Ditrogonal prism: A ditrigonal prism is very similar to the trigonal prism but this form has six faces instead of three. Once again, these faces are parallel about a 3-fold rotation axis.