Atomic number: 59
Category: lanthanoid metal
Density at 25°C: solid: density: 6.779 g·cm−3
Praseodymium is quite reactive in it's pure element form and tends to form oxides very easily, a sort of greenish coating. This is where it also gained it's name, prasios is Greek for green. It tends to be found in minerals almost exclusively. It is quite handy for optical uses like colouring glass and even as a doping agent to slow down light.
Use, natural applications or common combinations:
- some optics - used to to filter yellow light from light sources.
- alloys misch metal (an alloy of rare earth elements in various naturally occurring proportions)
- Standard atomic weight: 140.907 65(2)
- Melting point: 935 °C 
- Boiling point: 3520 °C
- Radioactivity: all stable