What mod makes it so difficult to find diamonds?

[namiasdf]

In my experience diamonds are used LESS in modded minecraft since you don't have tools\armor which will break to eat them. I always end up with far more than I can easily use, sure IC2 will use a lot but it allows you to make them so it balances out, once you have auto mining and\or a nicely Lapis'd TiC pick you should be swimming in the damn things.
If you still want to have more though as already stated Thermal Expansion allows you to adjust all ores that it knows about you can create an overworld that is effectively a dense ores age if you really wanted to.

Iridium plates, AE, logistics pipes, etc. Though you aren't using diamonds for tools/armour, the same case can be said for all other materials. I don't remember the last time I made iron armour, nor do I intend on replace in my mining drill with an iron pickaxe.

 

[Saice]

diamond only spawns under Y 32 in the nether, and lava is at Y 32 too, so good luck finding any.

Unless you have a code snip-it to back that up as someone that does a vast majority of his mining in the nether these days by hand I know I have found many diamonds in the nether without any issues with lava and I'm fairly sure I have found them all over the place as far as Y axis is counted.

 

[Enigmius1]

Actually, what you are saying is partly true, because I have found no diamonds in my new world while in vanilla I would already have half a stack, although it might be bad luck.

It's only luck if you're not approaching it methodically. The game logic says that in every chunk there will be between x and y diamonds from bedrock to y=16. They're there. Unless you're gutting every chunk in the appropriate range, you can't say whether there are the "normal" amount of diamonds or not. When I'm starting a new world, one of my first main goals is to get a mine shaft to bedrock and start strip mining for resources, not because I have an anal retentive fixation with efficiency, but so I don't go frustrating lengths of time not finding what I need to progress because I'm spelunking or just clearing out a narrow band at some arbitrary level.

 

[Dravarden]

Unless you have a code snip-it to back that up as someone that does a vast majority of his mining in the nether these days by hand I know I have found many diamonds in the nether without any issues with lava and I'm fairly sure I have found them all over the place as far as Y axis is counted.

My mistake, I guess since last time I used nether ores, which was back in 1.2.5, it has changed.

 

[KingTriaxx]

Sorry, yeah, Treasure is the Thaumcraft equivalent to Fortune for wands.