(covers information from several alternate timelines)
Sand is a naturally-occurring granular material comprised of finely divided rock and mineral particles.
In an alternate timeline, Commander Charles Tucker III and Sub-Commander T'Pol had their honeymoon in cargo bay 3 of the Enterprise NX-01, which Tucker filled with sand they dug up from a passing asteroid. (ENT: "E²")
In 2269, while traversing the deserts of Lactra VII, Leonard McCoy complained that his shoes were full of sand, prompting Spock to note his apparent lack of scientific interest in his surroundings. (TAS: "The Eye of the Beholder")
By 2285, the atmosphere of Ceti Alpha V was dominated by, among other things, sand. (Star Trek II: The Wrath of Khan)
In 2354, Benjamin Sisko walked through hot sand on Gilgo Beach carrying lemonades and then stepped on Jennifer's towel to cool his feet. (DS9: "Emissary")
Burning noranium could be extinguished with sand. (TNG: "The Vengeance Factor")
The microbrain, an inorganic yet sentient lifeform discovered in 2364, lived in an area it referred to as "wet sand" – a soil layer near the water table of the planet Velara III. (TNG: "Home Soil")
Sand can be used in art to make sculptures. In 2378, Q claimed that the Continuum had "crumbled like a Gelbian sand sculpture" when he threatened to leave them unless they restored his son's powers. (VOY: "Q2")
Crossing a line of sand in a sumo match disqualifies a wrestler. According to Chakotay and Tuvok, Takashi lost the 77th Emperor's Cup because his knee broke the sand, though Kathryn Janeway remembered differently, stating that Takashi won that contest. (VOY: "Latent Image")