Kosher salt and sea salt are not the same. Kosher salt (or rock salt) is made up of the irregular and huge white grains from land salt mines. Kosher salt is coarser, less refined, and takes longer to dissolve. Also, it is less dense as it is composed of larger flakes.
On the other sea salt (or bay salt) has small, clear crystals of varying sizes, frequently inverted pyramid shapes, and is available in fine or coarse crystals. It is also the least processed of all the salts, and it is used in cosmetics as well as cooking. It is coarse, but it is not extremely dense because the flakes are not all the same size.