Appearances can be deceiving

Beauty is only skin deep as the saying goes.

The first thing you should learn is that the appearance (habit, morphology) of your crystal is not what is important. Beautiful looking crystals may not diffract and really ugly crystals might diffract excellently. The real definition of a “good” crystal is its diffraction pattern in the X-ray beam. Therefore, do not be misled by the appearance of your crystal–mount it and check it in the beam.

Beautiful crystals but poor diffraction

These hexagonal crystals of platelet-derived growth factor  diffracted to 6Å.

Ugly crystals that do diffract.

These crystals look like they are layered multiple crystals, but in fact they diffracted to 1.6Å. (Photo is courtesy of Dr. Alex Cameron, my office mate at the time.)

Moral of the story: no matter what it looks like, put the crystal in the beam.

Things that don’t even look like crystals sometimes diffract perfectly well. See the QUIZ at the end of the tutorials for an example.