crystal vs. glass vs. quartz
Don't mean to be a stickler here, but I think that maybe we need to define what each of these things are, because when you buy a globe that is labeled "genuine crystal" it might not be what you think it is.
First, glass, is indeed made from silica, and has the same molecular make-up as quartz crystal; it's just not in a crystalline stucture - it's actually in an extremely viscous liquid state. Most cheap stuff is made of glass. The often, but not always, have tiny bubbles or waves. The color is clear, but has just a slight aqua/greenish tinge.
If something is labled as "crystal" or "leaded crystal" or "fine crystal", then it is essentially glass that has had some lead added to it. The lead adds weight and gives more brilliance the higher the percentage of lead is. Swarovsky crystal is an example of this kind of "crystal." It must have a certain percentage of lead to be considerd "crystal," and a higher percentace to be called "fine crystal."These almost never have any sort of imperfection or even a tinge of color. They are "too" perfect, heavy, and they reflect light like crazy and are truly brilliant.
Quartz crystal, which is what I'm assuming that most of you want, will be almost as heavy as low-grade leaded crystal. And usually will have inclusions, sheets, rainbows, cracks, etc. They usually have a slight yellowish or white tinge. Even if they are "perfect," with no inclusions or cracks, they don't reflect light as brilliantly as fine crystal. They are a lot more rare, and are usually only carried in rock shops and metaphysical stores.
I'm no expert, but I have been a quartz-aholic for about 20 years, have some college experience with geology, and worked for a company that sold fine crystal items. I can usually judge what something is (glass, crystal, or quartz) just by looking and holding. I would venture to guess the little "crystal balls" at the drugstore are probably leaded crystal, though probably a lower grade (usually around 24%).
I also wanted to point out that all of these are silicon-based, and do not contain carbon - therefore, inorganic.