Thanks for the guide however I wanted to add that as other people have said there are in fact 5 gems in act 4-3. Not 3 or even 4 as the guide says. One in the second glowing wall, destroy all the barrels and boxes to get it. And another in the third glowing wall, again destroy all the barrels and boxes. The last one make sure you destroy the wall before destroying the two light barrels to the left of it as that triggers a cutscene.
There is in fact also another red gem that isn't in the guide and I have seen no one mention. Act 5-3 has 4 not 3. There is the one in the hanging corpse room. However there is also one in the barrel to the right of the cage holding the strawberry. To get this one though you may need to first go through the left and straight forward options of the maze and get the cutscene where Garcia and Johnson talk about Paula.
So yea great guide, however it's missing 2 gems and the fourth one on 4-3 isn't a maybe. It appeared in all 3 of my playthroughs.