Both top and broken off bottom have distinctive natural faceting that make this a great collector's item. I can't find its more specific name after various Google searches. It's not like the spherical type that's more common.
Yellow Selenite - not just tinged, but really yellow (even in segments) - is not a common find, especially if it's a Naica (the distinctive "angle-sawed" termination defines it as such). Instead of being 'merely' a channel stone, it's also grounding and body/belly connected.
It's very hard to find genuine Jet - forms of coal are being passed off as it - and especially large pieces are a real find. It's also a favorite of mine - this non-quarz-filled variety of Petrified Wood - because it's light density makes it an idea Healing, cleansing stone (to clear out inner gunk). Remember, we have much more OFFline than on, so Message us with your custom inquiries.