# 302-2 - GY 302 Crystallography and Mineralogy Supplementary...

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GY 302 Crystallography and Mineralogy Supplementary Lecture Notes 2 Crystal Systems and Symmetry Symmetry explanations below are from http://www.cartage.org.lb Plagioclase Triclinic 6 Gypsum, Orthoclase Monoclinic 5 Aragonite, Staurolite Orthorhombic 4 Quartz, Calcite Trigonal 3b Apatite Hexagonal 3a Zircon Tetragonal 2 Halite, Galena, Pyrite Cubic 1 Mineral examples Angles between axes Axes Crystal System 2-fold Rotation Axis - If an object appears identical after a rotation of 180 o , that is twice in a 360 o rotation, then it is said to have a 2- fold rotation axis (360/180 = 2). Note that in these examples the axes we are referring to are imaginary lines that extend toward you perpendicular to the page or blackboard. A filled oval shape represents the point where the 2-fold rotation axis intersects the page.

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http://www.cartage.org.lb 3-fold Rotation Axis - Objects that repeat themselves upon rotation of 120 o are said to have a 3-fold axis of rotational symmetry
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• Spring '11
• Staff
• Crystal system, rotation axis, Cubic Tetragonal Hexagonal Trigonal Orthorhombic Monoclinic Triclinic Axes Angles, 3-fold rotation axis, 6-fold rotation axis

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