I will attempt to answer this and dispell some of the totally ridiculous myths I have heard about LSD crystal purity.
First of all, I would like to point out that I am an x-ray crystallographer. My who job consists of crystallizing molecules. When I worked in organic synthesis, we used crystallization as a purification technique. When it comes to biomacromolecules, crystallization is much more difficult and you are far more likely to come across polymorphs.
The reason that different crystal forms of the same substance can exist, even if they are of the exact same purity, has to partly do with the kinetics of nucleation and crystal growth. Essentially, when a crystal is growing it is trying to arrange itself into a three-dimensional lattice with a minimum of energy. Biomacromolecules are more likely to exibit different crystal forms because they can arrange themselves into lattices of similar energy in a number of different ways. With small molecules like LSD tartrate, there are less ways that the crystal can arrange itself into a stable fashion, so it is less likely that you will run into polymorphs.
So, why do polymorphs exist? Some crystal forms will have approximately the same energy, but sometimes crystallization occurs fast or slow. If crysallization occurs quickly, then the crystal form which has the lowest potential energy barrier to overcome during its growth will be prefferred. However, if crystallization occurs slowly and is reversible, then the thermodynamically most stable crystal form will be preferred. There could then be a mix of kinetic vs. thermodynamic crystal forms in between the two extremes.
Those are not the only two factors in crystallization, even for the exact same substance. Solvation is known to play a role in crystallization, so often solvent molecules will be hidden in the intermolecular spaces of a crystal and will show disorder (and these buggers are damn hard to find sometimes with diffraction data). Solvation can also affect the kinetics of crystallization. That is, with one solvent, crystal form A might be kinetically preferred with one solvent but another solvent might prefer crystal form B.
It is entirely possible to have two very different looking crystals of the same substance with essentially the same purity, just as it is entirely possible to have two similar looking crystals of the same substance with very different purity. You can't tell just by looking!
However, even LSD is known to show crystal polymorphism. This means that, absolutely pure LSD tartrate exists in more than one crystal form.
Please see:
Neville, G A. et al. USP lysergic acid diethylamide tartrate (Lot I) authentic substance recharacterized for authentication of a house supply of lysergide (LSD) tartrate. Can. J. Appl. Spect. 37, pp. 149 - 157. (1992)
In fact,
However, according to our experience more than 50% of various EA derivatives examined within the last few years exhibit two or even more crystalline forms.
from:
Kren, V. and Cvak, L. (eds). Ergot: The Genus Claviceps. Harwood Academic Publishers, 1999. p.285.
EA = "ergot alkaloid"
Furthermore, I will say this. The idea that someone can tell crystal purity by visual inspection alone is complete and utter bullshit. I have seen substances that usually crystallize into beautiful pure white crystals precipitate as purple coloured garbage under the exact same conditions (as far as I can control for, at least). Of course, my first thought upon seeing something like that, is "Oh, my sample sucks. I may as well get rid of it." Further analyses can be very surprising. In this case, it was less than 2% impurity disrupting the crystallization process and adding the purple colour.
I have also seen beautiful crystal that give such garbage diffraction patterns that the purity must have been far below 50%, even though the crystal looked just like the pure ones that gave good diffraction data.
I suggest that you take the "needlepoint, fluff, etc." reports with more than a few grains of salt. It's complete nonsense.