Ordinary black board chalk is made up of ________.

Answer

To answer the question "Ordinary black board chalk is made up of ________," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Composition of Chalk**:
- Chalk is commonly used on blackboards for writing. It is important to know what materials are typically used to make chalk.

2. **Research the Chemical Composition**:
- Ordinary blackboard chalk is primarily composed of calcium sulfate. The specific form of calcium sulfate that is often referred to in this context is gypsum.

3. **Understanding Gypsum**:
- Gypsum is a mineral composed of calcium sulfate dihydrate, which has the chemical formula CaSO4·2H2O. This means it contains calcium sulfate along with water molecules.

4. **Conclusion**:
- Therefore, ordinary blackboard chalk is made up of gypsum, which is essentially calcium sulfate dihydrate.

### Final Answer:
Ordinary blackboard chalk is made up of **gypsum**.

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