The structure of table salt crystals is cubic. This means that the crystal has three axes at right angles and of equal length. Rows of alternating sodium and chlorine atoms are laid out along these axes. The resulting crystals have six square faces at right angles to each other.
Salt crystals come together this way because the sodium and chlorine that make them up have a very tight ionic bond, and the atoms are packed tightly together. Pure salt crystals are colorless, but impurities can make them yellow, red, brown or black. Sometimes the crystals are stepped or hopper-shaped.
Salt crystals are quite soft, with a hardness between 2 and 2.5 on the Mohs scale. They have a low density and specific gravity of about 2.17. They are of found in sedimentary rocks either as crystals, grains or masses. They're also embedded with clay. Sometimes they form great domed or arched deposits known as diapirs. However, salt crystals are mostly harvested from evaporated seawater.
Salt crystals dissolve easily in water and are good heat conductors. Salt is also necessary for the health of both humans and other animals. It's vital for the food preparation industry and is also used to make soda, sodium and hydrochloric acid.