Difference between revisions of "Crystallography"

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{{edit|--[[User:Doos|Doos]] 08:00, 4 December 2006 (PST)}}
 
{{edit|--[[User:Doos|Doos]] 08:00, 4 December 2006 (PST)}}
  
Tradionally crystallography is the study of crystals and describing them according to geometrical observations. This involves the measurement of imaginary crystal axes and symmetry. <br />
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Tradionally crystallography is the study of crystals and describing them according to geometrical observations. This involves the measurement of the crystal faces in relation to the imaginary crystal axes with the use of a goniometer and [[symmetry]]. <br />
 
In modern times crystallography is the study of atom arrangements in solids through x-ray diffraction photography.
 
In modern times crystallography is the study of atom arrangements in solids through x-ray diffraction photography.
  

Revision as of 09:35, 4 December 2006

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--Doos 08:00, 4 December 2006 (PST)

Tradionally crystallography is the study of crystals and describing them according to geometrical observations. This involves the measurement of the crystal faces in relation to the imaginary crystal axes with the use of a goniometer and symmetry.
In modern times crystallography is the study of atom arrangements in solids through x-ray diffraction photography.

Some solids do not have a structured arrangement of atoms and we name them "amorphous", like for instance glass and opal.

A crystal is a:

  • geometrical solid bound by flat surfaces
  • it has a regular and symmetrical pattern of atoms ('crystal lattice')
  • physical and optical properties may vary with direction

An amourphous solid has:

  • no definite shape ('not crystalline')
  • physical and optical properties remain the same in every direction

Ideally single crystals can be observed with the unaided eye, some crystals however are so small they can not be detected without magnification. Often these small crystals bind together to form a solid and we name them polycrystalline (poly = many).
Tradition divided polycrystalline structures into microcrystalline and cryptocrystalline.

Microcrystalline bodies are composed of crystals that can be individualy observed with magnification (as a microscope).
Cryptocrystalline substances are made up of such small crystals that the microscope can not distinguish individual crystals.
With modern microscopes, that can magnify upto 0.3nm, the term cryptocrystalline has become obsolete.

According emperical observations we devide crystals in 3 groups and 7 crystal systems.
It should be noted that some gemological institutes (as the GIA) do not consider the trigonal system as a system on its own, rather they classify it as a subgroup of the hexagonal system.

Crystal system Group
Cubic (isometric) I
Tetragonal II
Hexagonal II
Trigonal II
Orthorhombic III
Monoclinic III
Triclinic III