I’m pretty sure formal is not
That is called a mineral. Hope this helped.
Rural- relating to, or characteristic of the country side rather than the town. For a more simple definition it's basically people who live out in the country side. Example- She lives in a rural area.
The difference between a dry climate and a tropical climate is that the dry climate as you know is dry and the tropical climate is moist and wet, the compare is tropical wet climates receive much more rain than tropical dry climates do. However, the term “tropical wet and dry climate” actually refers to a single type of climate. Tropical dry climates occur in deserts, while tropical wet climates usually occur along the rainforest belt.