_______ (Diamond /graphite) is used as a lubricant.

Explanation

**Step-by-Step Solution:**

1. **Identify the Options**: The question provides two options: Diamond and Graphite. Both are allotropes of carbon.

2. **Understand Allotropes**: Allotropes are different forms of the same element, where the atoms are bonded together in different ways. In this case, diamond and graphite are two distinct forms of carbon.

3. **Analyze the Structure of Graphite**: Graphite has a layered structure. It consists of sheets of carbon atoms arranged in a hexagonal pattern. These layers are held together by weak van der Waals forces.

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