Powder Simulation

Look into GPU particles. You dont really need to use mesh for sand grains so you can just create grain-shaped GPU particle sprites and have hundreds of thousands of them.

How would I go about a sand simulation (in general powder simulation). Can I just generate 100’000 sand grain meshes or is there a better way to do this?

Kind Regards,

Ok, and do they collide with other meshes??

Yes. Check out Content Examples project, there are examples of GPU particles with collision in it.