what is the green stone in the tomb?

it was their Dilithium crystals

@hunter newcomb; Basically, it is a larger type chestburster (like the one that came out of Kane in Alien), it's still a baby it will grow into something huge.

I believe personally that the green stone keeps the goo and the vases dormant. (under control) I believe that when the engineers were running they were running to the ampule room, because something had gone wrong with the vases and the goo, so to keep it under control they ran to the room , but obviously due to results did not fix thier problem which resulted in their death. Possibly a devon or some sort of xenon organism was created due to this outbreak which later killed all those engineers. The engineers are obviously an extremely smart race, and i feel as if they almost sacrificed themselves for that one engineer in the movie, i feel as if they always have a plan, and they have a large agenda we don't know about.... yet.

yeah, the kryptonite like crystal certainly seems like it could be a big deal which has been highly overlooked...it could be an energy source, it could hold information like a hard-drive would, or it could be simply like kryptonite to the black goo organisms... Is there anything special hidden inside that monolith head? Did the engineers know that the deacon xeno would be their end? Was the last engineer really pissed off or did David provoke him...or better yet...the last engineer didn’t really seem that pissed off until the guy with the gun struck Elizabeth Shaw with the butt of it after having been ordered to by old man wayland...did anyone else notice that after that happened the engineer rose to his feet and his pupils turned black...and then he started ripping heads off?

It's part of a control for the temple. There is a system that keeps things dormant and climate controlled in there (see how no worms had eaten the head, nor bacteria rotted it, in 2000 years?). It senses intruders, and activates countermeasures (like slamming giant doors down). I was wondering about the shape of it, if it would be a humoid hand, or something more like a Xenomorph claw that activates it.. David didn't provoke the Space Jockey. Weyland did.

THat particular pyramid has vast amounts of unexplored space,,,perhaps secret areas not explored by the pups. There were several more Pyramids not even(as far as we know0 looked at by our surviviours.. The missing Engineers is to tied to what was chasing the Engineres in the hologram. I bet there is a secret escape outlet in the Big Head room perhaps even underground through the green crystal table,

More importantly the hologram showed other engineers entering, the last one being decapitated - the door closed behind them. So where are they? If the scanner pup went in, scanned, and left out of the same entrance then the room had no other in's our outs. There should have been more engineers in there.

Rhe green stone was a 'touchstone' that would attact an entity that made it thios far into theor sacred room. It's purpose is to unleash additional security measures,,destroy the invader and then rest in peace until activated again..Aassured that the sacredness of this temple was secured for another 2000 years.

"There should have been more engineers in there." Yes!