Crystallography Online: the website of the International Union of Crystallography

PS to yesterday's note:

> One property of a molecule is that it is composed of atoms.

  Even better would be:

      A molecule is a set containing atoms and molecules.

      It might be advisable to add the restriction that an atom, as an
individual member, may only occur in one molecule. This restriction
definitely does not apply to the non-molecular tectons or 'building
blocks' as in the quartz example.

H.