Crystal Systems

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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


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