Crystal Systems
crystal system
A scheme by which crystal structures are classified according to unit cell geometry. This geometry is specified in terms of the relationships between edge lengths and interaxial angles.
Double Pyramid - Tetragonal
Anatase Scheelite
Six-sided prism column - Hexagonal
Apatite
Tabular - Tetragonal
Apophyllite
Tabular (Rhombic) - Orthorhombic
Barite, Andalusite
Hexagonal Prism - Hexagonal
Beryl
Rhombohedron - Hexagonal
Calcite, Siderite and Dolomite
Disphenoids (psuedo-tetrahedron) - Tetragonal
Chalcopyrite
Pseudo-hexagonal - Monoclinic
Chlorite
Elongated Rectangular Prism - Orthorhombic
Columbite
characterizes itself by its three equivalent crystallographic axes perpendicular to each other.
Cubic or Isometric
Dodecahedron - Isometric
Garnet
Octahedron - Isometric
Gold Spinel Magnetite
Tabular - monoclinic
Gypsum Spodumene
Hexahedron - Isometric
Halite Galena Fluorite
based on four crystallographic axes. Three of the axes (denoted by a1, a2, and a3) are of the same length and lie in the hexagonal (basal) plane at 120° to one another (between the positive ends). A fourth axis (c), longer or shorter than other three, is perpendicular to this plane.
Hexagonal
Columns or prismatic - monoclinic
Hornblende Epidote
Trapezohedron - Isometric
Leucite Analcite (Analcime) Garnet
Tabular (6 sided) - Orthorhombic
Marcasite
Tabular 6 sided - monoclinic
Mica
referred to three unequal axes. Two of these axes (a and c) are inclined toward each other at an oblique angle; these are usually depicted vertically. The third axis (b) is perpendicular to the other two and is called the ortho axis. The two vertical axes therefore do not intersect one another at right angles, although both are perpendicular to the horizontal axis.
Monoclinic
Tabular (8 sided) - Orthorhombic
Olivine
referred to three mutually perpendicular axes, each of which is of a different length than the others
Orthorhombic
Pyritohedron - Isometric
Pyrite
Tabular - Hexagonal
Pyrrhotite
Hexagonal Prism and Rhombohedron - Hexagonal
Quartz
Tabular - Triclinic
Rhodonite Axinite Feldspar
Prism and Pyramid - Tetragonal
Rutile Scapolite Cassiterite Zircon
referred to three mutually perpendicular axes. The two horizontal axes are of equal length, while the vertical axis is of different length and may be either shorter or longer than the other two.
Tetragonal
Tetrahedron - Isometric
Tetrahedrite Sphalerite
Rhombic Columns -Orthorhombic
Topaz Natrolite
Trigonal Prism - Hexagonal
Tourmaline
referred to three unequal axes, all of which intersect at oblique angle and sometimes called the anorthic system because there are no angles that are orthogonal.
Triclinic
Cubic or Isometric
a = b = c α = β = γ = 90°
Hexagonal
a = b ≠ c α = β = 90° γ = 120°
Tetragonal
a = b ≠ c α = β = γ = 90°
Orthorhombic
a ≠ b ≠ c α = β = γ = 90°
Monoclinic
a ≠ b ≠ c α = γ = 90° ≠ β
Triclinic
a ≠ b ≠ c α ≠ β ≠ γ ≠ 90°
6 crystal systems
cubic, tetragonal, hexagonal, orthorhombic, monoclinic, triclinic
Double-wedged shape - monoclinic
sphene
