List the important sources of sulphur.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Forms of Sulfur**: Sulfur primarily exists in nature in the form of sulfates and sulfides. This is crucial for identifying its sources.

2. **Listing Important Sulfates**:
- **Gypsum**: This is a common sulfate mineral with the chemical formula CaSO4·2H2O. It is widely used in construction and agriculture.
- **Epsom Salt**: Known chemically as MgSO4·7H2O, Epsom salt is used in various applications, including gardening and health.
- **Barium Sulfate**: Represented by the formula BaSO4, it is often used in medical imaging and as a pigment.
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