Physical Properties of Promethium and Niobium
Melting Point
1,042.00 °C
  
99+
Boiling Point
3,000.00 °C
  
31
2,468.00 °C
  
99+
Appearance
  
  
Physical State
Solid
  
Solid
  
Color
Unknown
  
Gray
  
Luster
Metallic
  
Metallic
  
Hardness
  
  
Mohs Hardness
Not Available
  
Brinell Hardness
Not Available
  
Vickers Hardness
Not Available
  
Speed of Sound
Not Available
  
3,480.00 m/s
  
21
Optical Properties
  
  
Allotropes
No
  
No
  
α Allotropes
Not Available
  
Not Available
  
β Allotropes
Not Available
  
Not Available
  
γ Allotropes
Not Available
  
Not Available