Crystal (mineral)

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A solid material that exists as a 3-dimensional arrangement of atoms, ions or molecules in repeating patterns. Based on the orientation and positions of the repeating units, crystals are grouped into six systems:

  • isometric (cubic) - three perpendicular axes of equal length
  • tetragonal - three perpendicular axes, two of equal length
  • orthorhombic - three perpendicular axes of different lengths
  • monoclinic - three axes of different lengths, two perpendicular
  • triclinic - three axes of different lengths, none perpendicular
  • hexagonal - three symmetrically spaced axes in one plane with a fourth axes that extends perpendicular to the first three.

The morphology of a crystal affects its optical properties such as index of refraction, color and birefringence.

Synonyms and Related Terms

crystals; cristal (Esp., Fr., Port.); Kristall (Deut.); kristal (Ned.)

Resources and Citations

  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Walter C. McCrone, John Gustave Delly, The Particle Atlas, W. McCrone Associates, Chicago, IV, 1972
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998