Crystals are how minerals arrange themselves. Although there are more than 120 elements in the periodic table only 10 are present in the Earth’s crust in large amounts, so that means these elements are the ones we find most commonly in minerals (& crystals). Of these elements two – silicon and oxygen – are the most common and we find both in most minerals.
So, minerals are just naturally occurring solids that have a distinct chemistry and a typical crystal arrangement. We find silicon and oxygen in most minerals, along with the other abundant elements such as calcium, magnesium, aluminium, potassium etc and some of all the others.
Salts are just compounds of elements.