Praseodymium

In nature, praseodymium is found in the Earth's crust, 5.5-9.1 ppm, in rare earth minerals [4]. The isotope found in nature is ¹⁴¹Pr (100 %, stable) [4].

In pure solid form, praseodymium exist in the following forms:
α-form: hexagonal crystal at < 798 °C [4]
β-form: body-centered cubic crystal at > 798 °C [4]