“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