The strength of boron depends on its allotrope. Here are some of the key allotropes and their strengths:

1. Crystalline Boron (α-Boron):

- Hardness: 9.5 on the Mohs scale (comparable to diamond)

- Compressive Strength: Approximately 45 GPa (gigapascals)

2. Amorphous Boron:

- Hardness: Approximately 7.5 on the Mohs scale

- Compressive Strength: Around 10-20 GPa

3. Boron Carbide (B4C):

- Hardness: About 9.3 on the Mohs scale

- Compressive Strength: Approximately 35-40 GPa

4. Boron Nitride (BN):

- Hexagonal Boron Nitride (h-BN):

- Hardness: Around 4 on the Mohs scale (similar to graphite)

- Compressive Strength: Approximately 11 GPa

- Cubic Boron Nitride (c-BN):

- Hardness: 9 on the Mohs scale, making it one of the hardest materials known, second only to diamond.

- Compressive Strength: Approximately 16-18 GPa

These values are approximate and can vary slightly based on specific testing conditions and material properties.