Black diamonds are called:

Explanation

**Step-by-Step Solution:**

1. **Identify the Subject**: The question asks for the name of black diamonds.

2. **Define Black Diamonds**: Black diamonds are a specific type of diamond that is characterized by their black color.

3. **Common Name**: The common name for black diamonds is "carbonado."

4. **Characteristics of Carbonado**:
- Carbonado is recognized as the toughest form of natural diamond.
- It is an impure form of polycrystalline diamond.

5. **Composition of Carbonado**:
- Carbonado consists of a mixture of diamond, graphite, and amorphous carbon.

6. **Conclusion**: Therefore, black diamonds are scientifically referred to as carbonado.

**Final Answer**: Black diamonds are called carbonado.

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