This site is a lecture by Dr. Stephen Nelson from Tulane University that discusses the various nonstandard forms of crystal growth that are characteristic to some minerals. Topics include twinning (contact and penetration, polysynthetic and cyclical), the origins of twinning, and twin laws in the triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, and isometric systems. Various types of polymorphism in many minerals are discussed as well as polytypism, metamict minerals, mineraloids, and pseudomorphism. Examples of each mechanism in common minerals are given.
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Part of the Cutting Edge collection. The NAGT/DLESE On the Cutting Edge project helps geoscience faculty stay up-to-date with both geoscience research and teaching methods.
