Half-exposed ovoid emerald in the ampule room

@Big Dave 

Just to finish the statue in Rio is a welcoming redemptive pose with christ's face looking out and welcoming offering redemption. The crucifio images have that all important down cast "lost" pose where the face drops into the shoulders"  which is reflected in the sacrificial Deacon pose with its beautiful head stooped and in full view.

Right thats it I really must exercise more self discipline, though I congratulate you for going over and over the same ground with others.      

Or Steve just thought it looked cool when he sculpted the head that way :)  I actually think he intended the relief to come across as facing forward though. This is his 3D sculpt. Notice the 'eye' indentations.

@Nathan Adler - "Can you please provide the reference where "One of the designers said it was also a monument to science, art and religion"?"

Here is one.

https://www.washingtonpost.com/news/acts-of-faith/wp/2016/08/09/the-many-meanings-of-rios-massive-christ-statue/?utm_term=.9b6e03a87c35

Indeed i can see the  other side of the coin if we try and connect the Brazilian Christ the Redeemer Statue as Christ with open arms to embrace his followers and to embrace peace.

But then how does this apply to the Deacon Mural if we suppose the pose is in a form of open armed welcome and embrace....?

I did  a few posts back try and offer how we can look at it as this, but i see it still when i take the other side of the coin as the Engineers Embracing the Mural and not the Organism in the Mural actually demanding or implying the Engineers Should embrace it...

But then i guess the same can be said with the Christ the Redeemer Statue.... it may not say that its from Christ saying Embrace Peace and Embrace Christianity in my Name.

But maybe more those who created the Statue saying "look lets Embrace Christ, and this monument is their so we can Embrace Christ in the name of Good Will and Peace"

If we look at it like that and then take the view of those who built the Statue and apply that to the view of those who build the Mural in Prometheus, then i kind of can see how this could be.  

"But then how does this apply to the Deacon Mural if we suppose the pose is in a form of open armed welcome and embrace....?"

I don't recall anyone saying the pose of the alien figure in the mural was in the form of open armed welcome and embrace. I stated what I think the mural means (in my mind) several posts above.

Steve Messing was designing this room back when they were working with the Spaith's script, when when what became the Deacon was the Ultramorph. He designed and made the 3D sculpt for the mural. He is also the only one who has really said anything about the altar and mural:

• The altar area was meant to pay homage to Giger.

• The mural included some 'easter eggs', which were the early Giger face hugger designs that were not used in the original film, and maybe some queen visual reference (although he never said "queen")

• He thought an Engineer had sacrificed himself to create the ultramorph using the virus. In his words, that was an earlier, purer form of the xenomorph.

• The mural had a relief sculpture that gave the impression of an alien form with flowing structures surrounding it. He said this was the ultramorph.

• The Engineers worshipped the ultramorph. The mural was a religious sculpture.

That is all he said about it. Even though the ultramorph was later changed to the Deacon in the Lindelof drafts, that really does not require altering his back story on the mural. But it only seems to be HIS back story. That said, Messing's explanation works perfectly for me.  

I think trying to come up with deeper meanings for a piece of set dressing that is not in the script and practically never mentioned by the writers or director, is just making up your own fiction. Nothing wrong with that, but it does not appear they had any deeper thoughts on it, just Messing.

The altar and green gen is another story though. Ridley obviously had something in mind when he changed the bowl to the gem. It could have just been that visually he wanted something more interesting, or it could be that he and the writers had an idea for back story involving the gem, to be developed later.