Hi Joy, Yes, I agree that it is very difficult to distinguish those and it is even more difficult to put it in words or in writing: experts have been talking about shininess, transparency (rather than brown colour) and birefringence as far as I know. All these methods have some grain of truth in them, yet none is as simple let alone as accurate as we would like to believe. So, it seems to me that the only way to distinguish is what I would call the "operational" way, i.e. to streak seed from that precipitate into a couple of drops set at very similar conditions but that are just below the spontaneous nucleation level of supersaturation: if something grows along the streak line, the precipitate was microcrystalline. However, if it doesn't, that doesn't mean that it was not microcrystalline? Dilemma?
Another interesting question that you are raising is what are quasicrystalline or "ordered precipitates" really worth, in terms of ultimate success near the relevant conditions... Finally, how about these fluorescent pens? I have not had a chance to use one of these, but my feeling is that they would only really work on good-sized crystals. It would be very interesting to hear members' experiences with these on smaller stuff. Best, Emmanuel ----- Original Message ----- From: joybeiyang To: CCP4BB@JISCMAIL.AC.UK Sent: Thursday, June 10, 2010 9:06 AM Subject: [ccp4bb] How to distinguish microcrystalline, quasicystalline and precipitation? Hi everyone, I am preparing a "crystallization manual" for our group, however, I found that it is very difficult to distinguish microcrystalline, quasicrystalline and precipitation, especially when the precipitation was shiny, like the grit on the beach. Is there a way to distinguish the three? Comments and suggestions will be greatly appreciated! ------------------------------------------------------------------------------ Joy
