Boron
Physical properties
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Physical state @ 20°C:
Solid [5]
Color:
α-rhombohedral structure: Clear red crystals [7]
β-rhombohedral structure: Black [7]
α-tetragonal structure: Black, opaque with metallic luster [7]
Amorphous form: Black or dark brown [7]
Odor:
Odorless [5]
Molecular weight (g/mol):
10.811(7) [2]
Melting point (°C):
2092 [2]
Boiling point (°C):
4002 [2]
Ignition temperature (°C):
700 [5]
Density (g/cm
3
):
α-rhombohedral structure: 2.46 [7]
β-rhombohedral structure: 2.65 [7]
α-tetragonal structure: 2.31 [7]
Amorphous form: 2.350 [7]
Hardness:
Mineral hardness:
11 [2]
Solubility:
Water: Insoluble (20 °C) [5]