# Is a typical glass slide really amorphous or does it just have very small crystallites?

I heard today that there's not really any true amorphous materials; that the theoretical concept (no level of ordering whatsoever) exists of course, but that no materials are 100% truly random and always have some crystallites, even if they're really small.

Is that true, let's say, in the case of a typical glass microscope slide? (I know there are different grades and makes of glass, but the slide is probably a fairly standard type.) I briefly Googled "is glass actually amorphous" and "crystallite size in glass slide" but that didn't answer my question.

So what's probably the order of magnitude of the largest dimension of the average crystallite, if it has any to speak of?

However in molten silica the SiO$_2$ molecules polymerise with each other to form random chains. These chains start small and grow in a random fashion as the temperature falls. These chains tangle up with each other, and because they are large polymers they can't relax and crystallise as the temperature falls. It is possible to crystallise glass, but it requires very, very slow cooling. For example quartz crystals can form from the melt in granite.