From The Gemology Project
Crystal Systems & Forms
Crystal System

Diagram

Examples

Cubic
The cube is composed of 6 square faces
at 90 degree angles to each other. Each
face intersects one of the crystallographic
axes and is parallel to the other two.


Diamond
Garnet
Spinel

Tetragonal
The tetragonal system also has three axes
that all meet at 90°. It differs from the
isometric system in that the C axis is longer
than the A and B axis which are the same length
that all meet at 90°. It differs from the isometric
system in that the C axis is longer than the A
and B axis which are the same length.


Zircon

Hexagonal
In the hexagonal system we have an additional axes,
which gives the crystals six sides. Three of these
are equal in length and meet at 60° to each other.
The C or vertical axis is at 90° to the shorter axes.
Mineralogists sometimes divide this into two systems,
the hexagonal and the trigonal, based on their external
appearance, as follows:


Aquamarine
Benitoite
Beryl
Citrine
Emerald
Heliodor
Morganite
Quartz
Ruby
Sapphire

Trigonal
Again, the trigonal system is a subsystem of the
hexagonal. Most gem references will list these as
hexagonal.


Amethyst
Corundum
Tourmaline

Orthorhombic
In this system there are three axes, all of which
meet at 90° to each other. However, all the axes
are a different length.


Alexandrite
Andalusite
Chrysoberyl
Iolite
Peridot
Tanzanite
Topaz
Varisite

Monoclinic
The above crystal systems all have axes sides
that meet at 90°. In the monoclinic system all
the axes are different lengths. Two of them,
the A and C axes, meet at 90°, but the third
one does not


Azurite
Diopside
Feldspar
Kunzite
Nephrite

Triclinic
In this system all the axes are different
lengths and none of them meet at 90°.


Turquoise
