In nature, manganese is found in the Earth's crust, 0.085 %, in minerals such as pyrolusite, hausmannite, manganite, manganosite and braunite. Also found in minute quantities in water, plants and animals . The isotope found in nature is 55Mn (100 %, stable) .
In pure solid form, manganese exist in the following forms:
α-form: body-centered cubic crystal at < ~710 °C 
β-form: cubic crystal at 710 to 1079 °C 
γ-form/electrolytic form: face-centered cubic crystal at 1079 to 1143 °C 
γ-form, stabilized at room temp: face-centered tetragonal crystal 
δ-form: body-centered cubic crystal at > 1143 °C