The Seven Crystal Systems
Crystal shapes have been divided into seven groups or systems. There are also classes within each system, but for the sake of simplicity, I will not go into them here. Each system is determined by the crystal’s axes (plural of axis), and the angles at which these axes intersect. As this involves a good knowledge of geometry, I will touch only briefly on this area of identification. Some books also look at the basic two-dimensional structure that determines the symmetry of each shape, which will also be included, as it is easier to understand and remember.
In Crystal Power Crystal Healing, Michael Gienger ascribes a different personality type to each of the crystal systems. Although I don’t work in this way, I certainly recognise subtle differences in the qualities of each system. For example, as the cube represents earth in sacred geometry, cubic crystals are generally grounding, even those we would normally link with the upper or heavenly chakras for reasons of colour.
Cubic System (also known as the isometric system)
All three axes are of equal length and intersect at right angles.
Based on a square inner structure
Crystal shapes include cube (diamond, fluorite, pyrite), octahedron (diamond, fluorite, magnetite), rhombic dodecahedron (garnet, lapis lazuli – rarely crystallises), icosi-tetrahedron (pyrite, sphalerite), and hexacisochedron (pyrite).
Common Cubic Crystals: Diamond, Fluorite, Garnet, Gold, Pyrite, Silver, Spinel
Two axes are of equal length and are in the same plane, the main axis is either longer or shorter, and all three intersect at right angles.
Based on a rectangular inner structure
Crystal shapes include four-sided prisms and pyramids, trapezohedrons and eight-sided and double pyramids.
Common Tetragonal Crystals: Anatase, Apophyllite, Chalcopyrite, Rutile, Scapolite, Scheelite, Wulfenite, Zircon
Three out of the four axes are in one plane, of the same length, and intersect each other at angles of 60?. The fourth axis is of a different length and intersects the others at right angles.
Based on a hexagonal (6-sided) inner structure
Crystal shapes include hexagonal prisms (columns) and pyramids, twelve-sided pyramids and double pyramids.
Common Hexagonal Crystals: Apatite, Aquamarine, Beryl, Cancrinite, Emerald, Goshenite, Morganite, Sugilite, Zincite
Trigonal System (Rhombohedral System)
Axes and angles in this system are similar to the Hexagonal System, and the two systems are often combined as Hexagonal. In the cross-section of the prism base of a Hexagonal crystal, there are six sides. In a Trigonal crystal there are three sides the base cross-section.
Based on a triangular inner structure
Crystal shapes include three-sided prisms or pyramids, rhombohedra, scalenohedra.
Common Trigonal Crystals: Agate, Amethyst, Aventurine, Calcite, Carnelian, Chalcedony, Chrysoprase, Cinnabar, Citrine, Dioptase, Eudialyte, Hematite, Jasper, Magnesite, Phenakite, Quartz, Rhodochrosite , Rose Quartz (rarely crystallises) , Ruby, Sapphire, Smithsonite , Smoky Quartz, Tiger’s Eye, Tourmaline
Orthorhombic System (Rhombic System)
Three axes, all of different lengths, are at right angles to each other.
Based on a rhombic (diamond-shaped) inner structure
Crystal shapes include pinacoids, rhombic prisms, pyramids and double pyramids.
Common Orthorhombic Crystals: Alexandrite, Andalusite (Chiastolite), Anhydrite, Aragonite, Baryte, Celestite, Cerussite, Chrysoberyl, Danburite, Dumortierite, Enstatite, Hemimorphite , Iolite, Peridot, Prehnite, Purpurite, Sulphur, Tanzanite, Thulite, Topaz, Variscite, Zoisite
There are three axes, each of different lengths. Two are at right angles to each other and the third is inclined.
Based on a parallelogram inner structure
Crystal forms include basal pinacoids and prisms with inclined end faces
Common Monoclinic Crystals: Azurite, Brazilianite, Charoite, Chrysocolla, Crocoite, Diopside, Epidote, Gypsum, Hiddenite, Hornblende, Howlite, Jadeite, Kunzite, Lazulite, Moonstone, Muscovite (Mica), Nephrite, Neptunite, Orthoclase, Petalite, Serpentine, Sphene, Spodumene, Staurolite, Talc, Vivianite
All three axes are of different lengths and inclined towards each other.
Based on a ‘triclinic’ inner structure, meaning ‘three inclined angles’
Crystal forms are usually paired faces
Common Triclinic Crystals: Amazonite, Amblygonite, Aventurine Feldspar, Kyanite, Labradorite, Pectolite (Larimar), Rhodonite, Turquoise, Ulexite
No crystal structure.
Common Amorphous Minerals:
Amber (organic – not a mineral), Moldavite, Obsidian, Opal