Which allotrope of Carbon is hardest natural substance and highest melting point.

Explanation

To solve the question regarding which allotrope of carbon is the hardest natural substance and has the highest melting point, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Allotropes**:
- Allotropes are different physical forms of the same element. For carbon, the main allotropes include diamond, graphite, and fullerene.

2. **Identifying Natural Allotropes**:
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