Summary
The following table contains a selection of minerals gemologists may encounter as jewelry stones or gem specimens. The gems are sorted by their crystal system: cubic (isometric), tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, and triclinic.
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wulfenite - crystal system

These butterscotch-colored wulfenite gemstones show their tetragonal crystal structure. Some gems in the tetragonal crystal system form as rectangular prisms with square terminations, like these. Others can take the shape of rectangular prisms with pyramidal terminations. Some form as dipyramids, two 4-sided pyramids joined at their bases. Wulfenites on a limonite matrix, San Juan Poniente Shaft, Ojuela Mine, Mapimi, Durango, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.

“Amorphous” gems have no crystal structure.

Selected Minerals by Crystal System

Cubic Tetragonal Hexagonal Trigonal8 Orthorhombic Monoclinic Triclinic Amorphous
Almandine garnet Anatase Algodonite Agate Adamite Aegirine Albite Amber
Analcime Apophyllite Apatite Amethyst Aeschynite Actinolite Amazonite Glass2
Andradite garnet Carletonite Aquamarine Ametrine Alexandrite Augelite Amblygonite Moldavite
Bixbyite Cassiterite Benitoite Ankerite Andalusite Augite Andesine Obsidian
Boleite1 Chalcopyrite Breithauptite Aventurine Anglesite Azurite Anorthite Opal
Chromite Chiolite Cacoxenite Bloodstone Anhydrite Barytocalcite Axinite Petrified Wood
Cubic Zirconia (CZ)2 Ekanite3 Cancrinite Brucite Aragonite Bayldonite Bustamite Strass
Cuprite Fergusonite3 Catapleiite Calcite Barite Beryllonite Bytownite
Demantoid garnet Hyacinth4 Chlorapatite Carnelian Bismutotantalite Brazilianite Ceruleite
Diamond Idocrase (Vesuvianite) Covellite Chalcedony Boracite Canasite Chabazite
Fabulite (Tausonite) Leucite Emerald Chrysoprase Bornite Charoite Fowlerite
Fluorite Marialite Ettringite Cinnabar Brookite Chondrodite Kurnakovite
Gadolinium gallium garnet (GGG)2 Meionite Fluorapatite Citrine Celestite Chrysocolla Kyanite
Gahnite Meliphanite Goshenite Corundum Cerussite Clinochlore Labradorite
Gahnospinel Mellite Greenockite Davidite Chambersite Clinoenstatite Leucophanite
Galaxite Phosgenite Heliodor Dioptase Childrenite Clinohumite Montebrasite
Garnet Powellite Hydroxylapatite Dolomite Chrysoberyl Colemanite Nambulite
Gold Pyrolusite Jeremejevite Eudialyte Cobaltite Creedite Oligoclase
Grossular garnet Rutile Lizardite Gaspéite Cordierite Crocoite Pectolite
Hackmanite Sarcolite Manganapatite Hematite Danburite Cryolite Peristerite
Haüyne Scapolite Milarite Ilmenite Descloizite Datolite Pyrophyllite
Helvite Scheelite Mimetite5 Jasper Diaspore Dickinsonite Pyroxmangite
Hessonite garnet Sellaite Moissanite (Carborundum)6 Linobate (Lithium niobate)2 Dumortierite Diopside Rhodonite
Katoite Stolzite Morganite Lizardite Enstatite Durangite Serandite
Langbeinite Tugtupite Nepheline Magnesite Eosphorite Epidote Serendibite
Lapis lazuli Wardite Niccolite Melonite Euchroite Euclase Sunstone
Lazurite Wulfenite Painite Millerite Euxenite3 Friedelite Talc
Leucogranite Zircon3 Precious Beryl7 Parisite Goethite Gadolinite3 Tinzenite
Magnesiochromite Simpsonite Phenakite Grandidierite Gaylussite Turquoise
Magnetite Sogdianite Prasiolite Hambergite Gypsum Ulexite
Melanite garnet Sturmanite Proustite Hemimorphite Hedenbergite Weloganite
Microlite3 Sugilite Pyrargyrite Holtite Herderite
Pentlandite Taafeite Quartz Humite Hodgkinsonite
Periclase Thaumasite Rhodochrosite Hypersthene Hornblende
Picotite Vanadinite Rose quartz Kornerupine Howlite
Pleonaste Wurtzite Rubellite Lawsonite Huebnerite
Pollucite Zincite Ruby Libethenite Hureaulite
Pyrite Sapphire Lithiophilite Hurlbutite
Pyrope garnet Schlossmacherite Manganotantalite Inderite
Rhodizite Siderite Marcasite Jadeite
Rhodolite garnet Smithsonite Mordenite Kämmererite
Schorlomite Smoky quartz Natrolite Lazulite
Senarmontite Stichtite Norbergite Legrandite
Silver Tiger’s eye Peridot Lepidolite
Sodalite Tourmaline Prehnite Linarite
Spessartite garnet Willemite Purpurite Ludlamite
Sphalerite Samarskite3 Malachite
Spinel Scorodite Mesolite
Thorianite Sekaninaite Monazite3
Topazolite garnet Sepiolite Moonstone
Tsavorite garnet Shattuckite Muscovite
Uvarovite garnet Shortite Nephrite
Villiaumite Sillimanite Neptunite
Yttrium aluminum garnet (YAG)2 Sinhalite Orthoclase
Zunyite Stibiotantalite Palygorskite
Strontianite Papagoite
Sulfur Pargasite
Tantalite Petalite
Tanzanite (Zoisite) Phosphophyllite
Tephroite Prosopite
Thomsonite Psilomelane
Topaz Pumpellyite
Triphylite Pyrophyllite
Variscite Realgar
Wavellite Richterite
Witherite Rinkite
Zektzerite Sanidine
Sapphirine
Scolecite
Serpentine
Sphene (Titanite)
Spodumene
Spurrite
Staurolite
Talc
Tremolite
Väyrynenite
Vivianite
Vlasovite
Whewellite
Wolframite
Wollastonite9
Xonotlite
Yugawaralite

Notes

1. Boleite has also been classed as a tetragonal, pseudo-cubic crystal.

2. Synthetic, lab-created material.

3. May lose their crystalline structure due to radiation (metamictization).

4. In modern times, hyacinth or jacinth usually refers to reddish brown zircon, which belongs to the tetragonal crystal system. However, historically it has also been used to refer to hessonite (cubic), topazes (orthorhombic), and various other gemstones.

5. Mimetite has also been classed as a monoclinic, pseudo-hexagonal crystal.

6. Both natural and synthetic stones. (Natural moissanite crystals are too small to cut).

7. Any beryl variety not aquamarine, emerald, goshenite, heliodor, morganite, or red.

8. Many of the materials mineralogists have classed as trigonal crystals have been classed by gemologists as hexagonal crystals in a trigonal subclass. Thus, you’ll find many of the gems listed here classed as hexagonal in their individual gem listings.

9. Wollastonite has monoclinic and triclinic polytypes.

Additional Crystal System Information

For more detailed information, consult the individual gem listings as well as these International Gem Society articles:

What are Crystal Systems and Mineral Habits?

Descriptive Crystallography for Gemologists