"Phantom Crystals" can easily be achieved by failing to cryoprotect most 
any crystal, or by a few other common crystal handling methods, but I 
don't think this is what you were asking about.

I do have users bring in what I call "plastic crystals" from time to 
time, but these crystals that don't diffract a single spot are 
relatively rare. Once every month or two I see a new one. (not counting 
repeat visits from users who are cursed with them) I always advise doing 
a 180-degree oscillation in such cases because sometimes it is a salt 
crystal that just happened to not have any reciprocal lattice points on 
the Ewald sphere. If this reveals a symmetrical pattern of a few very 
bright spots, then it can only mean a salt crystal. But, once in a while 
there really is no diffraction at all, and the user is left to ponder if 
it really was a very bad protein crystal or just a chunk of plastic that 
fell into their drop. Repeating the setup is the only way to really know.

Also, I suspect that small beamstops reduce the number of samples that 
meet your criterion, as I have also seen plenty of crystals that don't 
diffract beyond 30 A, or even 50 A or 100 A, but still give off a few 
spots in a region that would be behind the beamstop on many 
diffractometers. Such samples are common enough that Ana Gonzalez has 
coined the term "BBC" (behind-beamstop crystallography) to refer to such 
experiments.

Another way to make a "phantom crystal" is with radiation damage. If you 
blast any crystal long enough, all the spots will go away, leaving a 
SAXS pattern around the beamstop:
http://bl831.als.lbl.gov/~jamesh/ribo_blast/diffraction.gif
How useful this SAXS pattern is for deducing structural information 
remains to be seen, but since even "naturally phantom" crystals must 
still contain atoms, and atoms scatter x-rays, then SAXS signal from 
such objects could be useful.

Nevertheless, I think it is still up in the air how much diffraction 
tends to be degraded by crystal handling vs crystals just being "born 
ugly", as the proper control (shooting crystals without handling them) 
has not been done on anything but a few test cases. In fact, I have 
heard enough stories about ugly crystals diffracting very well and 
beautiful crystals diffracting poorly to wonder if these two qualities 
really are anticorellated. That is, beauty really is just "skin deep" 
(and ugly goes to the core). I think it will be telling to see what sort 
of results we get from the now several available "in-situ" diffraction 
systems <shameless plug>one of which myself and others developed with 
Fluidigm, who are now selling them</shameless plug>.

-James Holton
MAD Scientist

George DeTitta wrote:
>
> 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.
>
> **George T. DeTitta, Ph.D.**
>
> **Principal Research Scientist**
>
> **Hauptman-Woodward Institute**
>
> **Professor and Chairman**
>
> **Department of Structural Biology**
>
> **SUNY at Buffalo**
>
> **700 Ellicott Street**** Buffalo NY 14203-1102 USA**
>
> **(716) 898-8600 (voice)**
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>