Crystal Systems

Crystal Systems

**Crystals are divided into seven systems. The individual system distinctions are made according to the crystal axes and the angles at which the axes intersect. There are also many sub-systems within these main categories. The Isometric and Cubic systems are the same system with alternative names. You may find an additional crystal system listed in some sources, which is the Amorphous system. Amorphous “crystals” have no crystalline structure because they cooled down too quickly to form any distinct shape. In this category you will find material such as volcanic obsidian varieties and meteoric tektites. Illustrations and descriptions of the seven systems are listed below.

Isometric ~ Cubic System: All three axes have the same length and intersect at right angles. The following crystal shapes can be found within this system: Cube, Dodecahedron, Octahedron, Trapezohedron, Diploid, Gyroid, Hexoctahedron, Hextetrahedron, Tetartoid, Tetrahedron, Tetrahexahedron, Trisoctahedron, Tristetrahedron, Deltoid Dodecahedron, and Pyritohedron.

Hexagonal System: Three of the four axes are in one plane, are of the same length, and intersect each other at angles of 60 degrees. The fourth axis, which is a different length, is at right angles to the others. The following crystal shapes can be found within this system: Dihexagonal Dipyramid, Dihexagonal Pyramid, Hexagonal Dipyramid, Ditrigonal Dipyramid, Hexagonal Pyramid, Hexagonal Trapezohedron, and Trigonal Dipyramid.

Trigonal System: (Rhombohedral System) Axes and angles are similar to the Hexagonal System, therefore the two systems are often combined as one system. There is a difference in their symmetry. In the Trigonal System the cross section of the prism base is three-sided. It is six-sided in the Hexagonal System. The following crystal shapes can be found within this system: Ditrigonal Pyramid, Hexagonal Scalenohedron, Trigonal Pyramid, Rhombohedron, and Trigonal Trapezohedron.

Tetragonal System: The three axes intersect at right angles, two are of the same length and are in the same plane, while the main axis is either longer or shorter. The following crystal shapes can be found within this system: Tetragonal Dipyramid, Tetragonal Disphenoid, Tetragonal Pyramid, Ditetragonal Dipyramid, Ditetragonal Pyramid, Tetragonal Prism, Ditetragonal Prism, Tetragonal Scalenohedron, and Tetragonal Trapezohedron.

Orthorhombic System: Three axes of different lengths are at right angles to each other. The following crystal shapes can be found within this system: Pinacoid, Rhombic Prism, Rhombic Dipyramid, Rhombic Disphenoid, Rhombic Pyramid, and Rhombic Tetrahedron.

Monoclinic System: The three axes are each of different lengths, two are at right angles to each other, and the third one is inclined. The following crystal shapes can be found within this system: Domatic, Prismatic, Sphenoid, and Pinacoid.

Triclinic System: All three axes are of different lengths, none of which are perpendicular and inclined to the others. Typical crystal forms are paired faces. The only regular forms recognizable in Triclinic crystals are the two parallel faces of the Pedion and the Pinacoid. The Pinacoid face has no symmetrical relationship to any other.

A Brief Guide To The Crystal Systems Of A Few Minerals

Isometric ~ Cubic

Almandite, Analcite, Andradite, Cubic Zirconia, Cuprite, Demantoid, Diamond, Fluorite, Gahnite, Garnet, Gold, Grossularite, Hauynite, Hessonite, Lazurite, Magnetite, Melanite, Periclase, Pollucite, Pyrite, Pyrope, Senarmontite, Silver, Sodalite, Spessartite, Sphalerite, Spinel, Strontium Titanate, Topazolite, Tsavorite, Uvarovite

Tetragonal

Anatase, Apophyllite, Boleite, Carletonite, Cassiterite, Chalcopyrite, Cristobalite, Idocrase, Leucite, Melinophane, Phosgenite, Pyrolucite, Rutile, Scapolite, Scheelite, Tugtupite, Wardite, Wulfenite, Zircon

Hexagonal

Apatite, Aquamarine, Benitoite, Beryl, Cancrinite, Catapleiite, Emerald, Goshenite, Greenockite, Heliodor, Jeremejevite, Milarite, Morganite, Nepheline, Painite, Sugilite, Taafeite, Thaumasite, Zincite

Trigonal

Agate, Amethyst, Aventurine, Calcite, Carnelian, Chalcedony, Chrysoprase, Cinnabar, Citrine, Corundum, Davidite, Dioptase, Dolomite, Eudialyte, Friedelite, Gaspeite, Hematite, Jasper, Magnesite, Parisite, Phenakite, Prasiolite, Proustite, Pyrargyrite, Quartz, Rhodochrosite, Rock Crystal, Rose Quartz, Ruby, Sapphire, Siderite, Simpsonite, Smithsonite, Smoky Quartz, Stichtite, Tiger’s Eye, Tourmaline, Willemite

Orthorhombic

Adamite, Alexandrite, Andalusite, Anglesite, Anhydrite, Aragonite, Barite, Boracite, Celestite, Cerussite, Chrysoberyl, Danburite, Descloizite, Diaspore, Dumortierite, Enstatite, Hambergite, Hemimorphite, Hypersthene, Iolite, Kornerupine, Lithiophilite, Manganotantalite, Meerschaum, Mesolite, Natrolite, Peridot, Prehnite, Purpurite, Sulfur, Sinhalite, Strontianite, Tanzanite, Tantalite, Thulite, Topaz, Triphylite, Variscite, Witherite, Zoisite, Zektzerite

Monoclinic

Aegerine-Augite, Azurite, Barytocalcite, Beryllonite, Brazilianite, Charoite, Chrysocolla, Clinohumite, Clinozoisite, Colemanite, Crocoite, Diopside, Eosphorite, Epidote, Euclase, Gaylussite, Gypsum, Hiddenite, Hornblende, Howlite, Jadeite, Kunzite, Lazulite, Legrandite, Malachite, Moonstone, Muscovite, Nephrite, Neptunite, Orthoclase, Petalite, Phosphopyllite, Sapphirine, Serpentine, Sphene-Titanite, Spodumene, Staurolite, Talc, Tremolite, Vivianite, Vlasovite, Whewellite, Yugawaralite

Triclinic

Amazonite, Amblygonite, Andesine, Aventurine Feldspar, Axinite, Kurnakovite, Kyanite, Labradorite, Microcline, Montebrasite, Oligoclase, Pectolite, Rhodonite, Sanidine, Turquoise, Ulexite

Amorphous

Amber, Ekanite, Moldavite, Obsidian, Opal

Complete Lists Of All Minerals & Their Crystal Systems

"Isometric System Minerals"

http://www.mindat.org/system_search.php?c=Isometric

"Hexagonal System Minerals"

http://www.mindat.org/system_search.php?c=Hexagonal

"Trigonal System Minerals"

http://www.mindat.org/system_search.php?c=Trigonal

"Tetragonal System Minerals"

http://www.mindat.org/system_search.php?c=Tetragonal

"Orthorhombic System Minerals"

http://www.mindat.org/system_search.php?c=Orthorhombic

"Monoclinic System Minerals"

http://www.mindat.org/system_search.php?c=Monoclinic

"Triclinic System Minerals"

http://www.mindat.org/system_search.php?c=Triclinic

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