What is the main difference between formal and informal organization structures?

Formal structures are not commonly used to explain the hierarchical structure of the organization, whereas informal structures depict the hierarchical structure

Formal structures outline the clear lines of authority through an org chart, whereas informal structures focus on how things get done day$-$to$-$day

Formal structures play a major role in creating an organizational culture, whereas informal structures do not influence organizational culture

Formal structures are easy to change, whereas informal structures are based on the org chart and are hard to change