Find a
Select grade level(s) Select resource type(s) Select collection(s) Select standard(s) Skip navigation Digital Library for Earth System Education
Digital Library for Earth System Education
Search tips
Twinning, Polymorphism, Polytypism, Pseudomorphism
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.
Intended for grade levels:
  • College (13-14)
  • College (15-16)
Type of resource:
  • Visual:
    • Illustration - scientific
  • Text:
    • Ref. material
  • Geological Sciences:
    • Geochemistry
    • Mineralogy or petrology
Technical requirements:
No specific technical requirements, just a browser required
Cost / Copyright:
No cost
Copyright 2001 Tulane University New Orleans, LA 70118
DLESE Catalog ID: SERC-NAGT-000-000-000-745
Related resources:
This resource is part of
Resource contact / Creator / Publisher:
Author: Dr Stephen A. Nelson
Tulane University