We do see these from time to time with users, but nobody pays
attention to them. It once happened to us a number of years ago.
They were perfectly good looking lysozyme crystals treated with heavy
metal soak. They diffracted fine when fresh, but failed to diffract
at all after a couple months of storage. I think Art Weaver studied
these kinds of cases years ago using electron microscopy to see if
there was any visible problem with the lattice.
Check this out: A.J. Weaver, A.W. McDowall, D.B. Oliver, and J.
Deisenhofer, J. Struct. Biol., 87 (1992).
In Art's case, he was able to extract lattice and packing info from
the FFT of the EM images (at 40 A).
Perhaps if he had access to a SAXS line, he would have seen Bragg
spots. Hard to know. It seems to me that there should always be some
anisotropic scattering at very low angles no matter how badly the
lattice is distorted.
Richard Gillilan
MacCHESS
BTW, I've also seen and harvested "ghost crystals" that were bubbles.
Folds of skin can look like crystal edges sometimes.
Speaking of ghosts, I had a dried out drop that looked just like a
statue of Buddha I thought. One of my students came upon one that
looked just like a couple of monkeys kissing. The ACA should host a
pareidolia contest someday.
I’d appreciate it if people could tell me their experiences with
what I would call “phantom crystals”, or “ghost crystals”. These
are objects that display the seeming morphology of crystals (clear
facets, sharp edges) but do not diffract X-rays AT ALL. I would
not count objects that diffract to 30 A in this category. I mean
objects that don’t show a single Bragg spot.
