I don't even know what it was.
I was walking around at night (like 2 AM) at Burning Man, tripping face on DOC and acid, and I saw a little plastic bag on the ground, so I picked it up because it was moop (matter out of place) and a citizen of Black Rock City always picks up moop. I didn't look at it until 15 minutes later ... I realized I'd just picked up 20 hits of acid, 2 capsules that looked like molly, and one mystery capsule with a tiny little bit of shard-like crystal powder kicking around inside.
I ate two hits (on top of one strong sugar cube and 2 hits of DOC from earlier that night), gave away the rest of the acid over the course of the night, hung out on a huge art car all morning after the sun came up drinking Bloody Marys and beer, and got just drunk enough (remember, still twisted on DOC at this point) to snort the mystery capsule.
It burned like a motherfucker and I was extra spun for 4 hours. My best guess is that it was some kind of 2C-X, because the effects felt psychedelic rather than speedy, dopey, or ketamine-like. Also, the quantity looked to be about right for a dose of 2C-X ... 15-20mg at most.
I had a great time. Don't do what I did, though. Snorting shit you found on the ground at Burning Man is not actually a good idea, even if I had fun doing it.