What is this Lake Michigan rock? Rock found along northern Lake Michigan, (Charlevoix, MI).  Made up of very thin crystalline layers. There are small, round bubble like bumps that protrude from the surface. Doesn't show well in the picture, but the rock has a sugary appearance.
I can't be definite but my three best guesses are Travertine, Agate and maybe Halite, if it fizzes in mild acid it's Travertine, a form of Limestone, if it dissolves in hot water it's Halite, or Rocksalt, otherwise if it's more or less inert it's probably Agate, an amorphous silicate. I find Halite unlikely, the other two are probably pretty equally likely in that location.