MINERALOGY CRYSTAL SYSTEMS

Symmetry Mirror Plane = imaginary plane that divides a crystal into halves, each of which is the mirror image of the other Axis of Rotation = imaginary line through a crystal about which the crystal may be rotated and repeat itself in appearance (1,2,3,4 or 6 times during a complete rotation)

Tips for creating models Write your name on each model BEFORE folding and taping! Cut “into” the pattern rather than “around” it. Fold along each face intersection BEFORE taping into place. Have fun learning something new!

Isometric System 90° ISOMETRIC  =  =  = 90° a = b = c c = a b = aa Pyrite, Galena, Halite, Fluorite, Garnet, Diamond    Unique Symmetry: Four 3-fold axes

Tetragonal System 90° TETRAGONAL  =  =  = 90° a = b  c c  a b = aa Wulfenite, Zircon, Chalcopyrite, Rutile    Unique Symmetry: One 4-fold axis

Hexagonal System 120° 90° HEXAGONAL  = 120°,  =  = 90° a = b  c c > a Quartz, Beryl (Emerald), Apatite, Graphite, Corumdum (Ruby, Sapphire) b = a    Unique Symmetry: One 6-fold axis a

Orthorhombic System 90° ORTHORHOMBIC  =  =  = 90° a  b  c c  a b  a a Sulfur, Barite, Olivine, Topaz    Unique Symmetry: Three 2-fold axes

Monoclinic System 90° MONOCLINIC  =  = 90°,   90° a  b  c c  a b  a a Orthoclase, Malachite, Azurite, Gypsum, Mica, Talc    Unique Symmetry: One 2-fold axis  90°

Triclinic System  90° TRICLINIC       90° a  b  c c  a Turquoise, Plagioclase Kyanite, Albite    Unique Symmetry: None  90° b  a a

Crystal Systems SystemAxesAnglesUnique SymmetryDiagramExamples Isometric a=b=c  =  =  =90° Four 3-foldPyrite, Halite, Galena, Garnet, Diamond, Fluorite Tetragonal a=b  c  =  =  =90° One 4-foldWulfenite, Rutile, Zircon, Chalcopyrite Hexagonal a=b  c  =120°,  =  =90° One 6-foldQuartz, Beryl (Emerald), Apatite, Corundum (Ruby, Sapphire) Orthorhombic a  b  c  =  =  =90° Three 2-foldSulfur, Barite, Olivine, Topaz Monoclinic a  b  c  =  =90°,  90° One 2-foldOrthoclase, Malachite, Azurite, Mica, Gypsum, Talc Triclinic a  b  c  90° NoneTurquoise, Kyanite, Albite, Plagioclase

Crystal Systems SystemAxesAnglesUnique SymmetryDiagramExamples Isometric Tetragonal Hexagonal Orthorhombic Monoclinic Triclinic