Tutorial 4: types of crystals

Remember: you can click on any picture to get a magnified view.

  Sea urchins. These often begin as spherulites (see previous tutorial) or grow from a spherulite. They are extremely thin needles clustered around a single nucleation site. Often they appear "fuzzy". The white arrows in this picture show three-dimensional crystals growing from independent nucleation sites in the same drop.
   Extremely thin needles growing from a single nucleation center. Since these needles are much longer, I would not call this a "sea urchin" any longer. Notice the large 3-D crystal growing in the same drop.
  Needles. Still too many but at least they are single needles. The nucleation rate is too high which is why you have too many, and too thin. Try reducing the protein or precipitant concentration or both. Another method is to put a layer of oil over the reservoir in the vapor drop set-up. (see Chayen , put reference here.)  See also the Tutorial 4 on seeding.
   Plates. Two-dimensional. Plates are usually considered an improvement over needles. These are growing from a single nucleation site and overlaying each other, which is far from optimal. Optimize to grow them as separately and thicker.
   A three dimensional crystal. But check the diffraction before you get out the champagne.

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