For day 21, a simple shot of something with an amazing and complex history.
Salt founded kingdoms in Europe, brought Italian city-states to war with one another, was interdicted by the British in the American Revolutionary War, and instigated a march by Gandhi. Salt was used as a weapon against a defeated foe, allowed intercontinental travel and was responsible for huge networks of roads in several ancient Empires. In the Bible, salt was referenced as a form of payment, and it coined the phrase 'salt of the earth'.
The history of humanity is tightly tied to these tasty little crystals.
ISO 100, f/16, 1/160th shutter on a blue background, with both flash and supplementary fill light.