| 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. |
|
|
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.
|
|
 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: |
|
|
Trigonal
Again,
the trigonal system is a subsystem of the
hexagonal. Most gem references will list these
as hexagonal.
|
|
 Amethyst
 Citrine
 Corundum
 Tourmaline
Eudialyte
|
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.
|
|
|
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.
|
|
|
Triclinic
In this system all the axes are different
lengths and none of them meet at 90°.
|
|
 Turquoise
|
Diamond
Garnet
Rhodolite
Spinel
Aquamarine
Benitoite
Beryl
Emerald
Heliodor
Morganite
Quartz
Ruby
Sapphire
Alexandrite
Andalusite
Chrysoberyl
Iolite
Peridot
Tanzanite
Topaz
Azurite
Diopside
Feldspar
Kunzite
Nephrite
