More specific than that, there are 4 qualities of crystal and 4 qualities of material. Each (in the correct order described above) correlates to the entire pool of that class of material. I.e. If there is only 1 G4 material in the planets crust, needle crystals will ALWAYS drop that. If there are three g3 materials available, crystalline clusters will always drop one of those, seemingly chosen at random (percentages of composition aren't obviously playing a role in my figures currently, from a fair sample size).