I used to work for a foreign company in the US that made this stuff. All the crucibles were made out of graphite, never saw a quartz crucible, maybe they are used in the making of them via ingredient or mold, or maybe they produce a different quality of silicon. We “grew” the silicon into these big (ranging from 2-4ish ft long) cylinder like crystals where they would be shipped off to another area to be sliced into thin wafers for chips. The crucibles were good for maybe I think under 100 runs before they needed to be replaced if they didn’t fail before that.