I had to look up "rock crystal". I'd never, ever come across the phrase before - even back when I was something of a rock hound and made a hobby of studying geology and collecting minerals.And yet, I'm still not convinced I've stumbled upon the correct usage here. Everything I'm finding suggests that "rock crystal" refers to high purity quartz - and yet if the object pictured here is made of quartz, I could only imagine from the appearance that it's a very impure variety, and one with a rather bizarre degree of uniformity at that.I'm utterly baffled. Purer quartz varieties are transparent - or at the very least translucent. And yet this is completely opaque, which surely means it must be impure? But even heavily worn or polished quartz has signature crystal faceting, particularly when purity is low - but that doesn't seem to be the case at all here. And it seems to be a remarkably uniform consistency, which doesn't make much sense if it's an impure quartz variety. And even the luster more closely resembles some weathered submetallic mineral, rather than being the the vitreous or waxy sort of luster you would get from quartz.It's frustrating that I can't find any other images of the piece to compare different angles or lighting. I very much want to assume that I'm the one who is mistaken here - after all, I'm a complete amateur and presumably this was collected and catalogued by experts. And yet I know full well even the best experts in the world can easily make clerical errors which then get carried forward with every citation and reference, compounding the issue as everyone simply copies and repeats information that ultimately comes from a single source.
Archaeologists are terrible at geology. A friend of mine once walked through a museum with a real petrologist. If the tag said, "Alabaster Vase," the petrologist would say, "that's not alabaster." "Onyx scepter" -- "That's not Onyx." And so on. On the brighter side, ancient peoples were also really bad at mineralogy. I was baffled by the Chinese use of "jade" for years -- besides the regular green jade, they have black jade, and red jade, and others, none of which are remotely the same mineral as the standard green jade. I finally figured out that in this context jade means "a stone suitable for carving by a master craftsman." It's a different kind of category from our mineralogy.So far as I can tell, Europeans used "rock crystal" to mean "colorless hard stone," and this usage has carried over into archaeology. Most "rock crystal" is quartz.
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