I have found a recipe which needs powdered mammoth tusk to create. At first I though it is possible to powder them with mills, but when I tried it I found out it wasn't. Have anyone idea how to powder them? Depending on the recipe it should be possible to do.

You take a mammoth tusk, and light it on fire! MUWAHAHAHAA!.... no, I really don't know... Kind of like the mystery with my Mammoth Cheese as well... I don't know how to do that. Giants do though!

you cant get human hearts or flesh out of the wealth of human corpses you make. (what about mer or beast race hearts btw? alchemy is racist)

you cant get ectoplasm from ghosts.

you cant get spriggan sap from spriggans (at least i havent found any)

some ingredients just cant be harvested from the source, however ridiculous that might be. you can rip out a daedra's heart in perfect condition, but you cant powder tusks...

Yeah that would be an epic unarmed bruce lee esque finisher * power attacks rips heart out* headbutts falling body spikes heart as if he just ran a touchdown.... Poses like a boss!

You can get ectoplasm from ghosts, it's just rare
Assuming sap would be the same thing for the higher Spriggans (like you I haven't found it outside of a shop / chest).

Did the recipe really need powdered mammoth tusk? o.O what recipe is that?

Well at least I have found ectoplasm from ghosts, spriggansap from spriggans (once) and I have found human hearts from Forsworn bodies.

Fear Poison:

~Powdered Mammoth Tusk

~Daedra Heart

Woah Daedra heart? Why would you make a potion out of that... Daedra Armor?!

Already been done on Indiana Jones.

Daedra hearts are sold regularly at the alchemists + light armor users have no purpose for Daedra Armor.

Ya but they are still good at filling up your pockets with useless septims though

At 50k septims or so, I stopped picking things up. Meh, wish they had made the economy a bit tougher, but they throw ultimate potions at you, and deathlords carry ebony.

Well I'll rather make armors from Dragon bones and scales. Septims from daedric armors are not worthy enough for me to waste three more perks on armorline I'm not using. It's too bad you can't get daedric-perk after Dargonarmor-perk. If you want to make daedric stuff you have to use perks for every perk on heavyarmorline.
Anyway I'm probably not making any of fear poison, I just want to get know how to powder tusks so I can see what else they can be used for. Daedric hearts are kind of rare ingredient to use because daedric creatures are so rare. I'm on level 40 and haven't seen any of non-summoned daedric creatures.