Yes, it's another round of that classic guessing game - Animal, Vegetable, Mineral, Abstract [or any combination thereof]. This effort - '03/'04 should address any queries, but then again, may just serve to confuse and baffle which some might say is the point of the game. Patience, integrity and a decent search engine may be useful ....
[d] I think you could say that any geological formation is primarily underground, even Mount Everest. If the question is whether it is entirely underground, the answer is no.
Moving quickly on a geological timescale, pausing only to thank the tectonic forces that fashioned this earth with the odd helping hand from extraterrestrial meteorites, read this carefully-arranged eruption which spells
ABSTRACT (as well as trouble for a few geological theories when it's discovered).
Welcome, welcome to one and all. [DrQ] It's abstract. Really quite abstract. So yes, if only in our minds. [Duj] Not the flat-earthers. [Boo] No Amazons here (with Black Friday coming, that may be a relief) [Raak] Not our twin from the dark side. [Gus] Topical in this epoch, but not relevant.
Lots of good stuff coming now. Both on the right evolutionary branch. [DrQuuxum] If you mean ems, ens and that sort of thing, no. [Raak] No, though in a sense, as you taught us to say, isn't everything?
[Boolbar] No "e" whatever, nothing to do with maths. Look, it begins with "b", it's short (hint: 3 letters), it's not a verb, a noun (notwithstanding a famous phrase in which it gets used as both a noun and a verb),or adjective and I'm regretting having used it. Not enough to give the answer?
Summary: mainly metal (but note the "strictly speaking" concerning the glass question), made now and before 1900 (perhaps predominantly the latter, judging by the audience reaction), can be larger than a toaster, not unique, not naturally occurring, no moving parts, not furniture, not a measuring device, not a kitchen item, not a lamppost.