No matter how hard I try, I can't transform a soulgem into a black sougem.

Tell me if I am wrong:
you have to put a gram soulgem (empty or with soul ???) on an altar, then cast a soul capture spell on it.

Well, I've tried, with soulgem on the altar, in the altar... can't transform it...

Maybe someone know the player.additem code ?

I had the same problem.And then it happened.......
You have to do it during night,and you there must be a purple light coming from the Altar.Then you place a grand Soul Gem (with or without a soul,it doesn't metter)and cast soul trap.Lowest quality soultrap will do just fine

Should be Player.AddItem 00000192 #

It doesn't just have to be done at night, it has to be done Either Tuesday Wednesday or Thursday, atleast two of those 3 days are correct, you can tell when to do it because a big light shines on the altar.

Woah... what exactly do the black soulgems do? I've seen them and held them and stuff but are they useful?

They are just grand soul gems that hold the souls of NPCs instead of creatures.

They are nice since you can kill some beggar or bandit to get a grand soul rather than searching out a really tough creature.

Cool! I wish soul gems still said the name of whatever you capture so I could have an "Adoring Fan Soulgem" Also... is there a quest where you learn how to make the gems or do you have to figure it out on your own (this forum?)

If you play through the mages guild... you will learn how they are made. By the time you finish it... you end up with an artifact that randomly creates/fills them whenever you kill an NPC.

Lol, that would be funny to have thier names... especially if someone modded the Emporer back in... think of it Emporer Grand Soulgem

I've been camping next to the shrine for a week... nothing happened, no light whatsoever... buguhhhh, gonna have to use console (hate cheating)

What shrine is that? Remember you don't see the special light very well in the daytime if you're close to the altars (at least I don't). You'll have to be some distance away from it.

And there is that note in the game that list all 4 altars. Can't remember which. The one that's called 'handwritten note', or 'hastily scribbled note'? Something like that...