Which of the following types of rocks is also known as natural glass?

Options

A. Gneiss
B. Obsidian
C. Basalt
D. Granite

Explanation

To solve the question "Which of the following types of rocks is also known as natural glass?", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify which type of rock is referred to as "natural glass."

2. **Review the Options**: The options provided are:
- A) Guinness
- B) Besselt
- C) Obsidian
- D) Granite

3. **Recall Rock Types**:
- **Guinness**: This is not a type of rock.
- **Besselt**: This does not correspond to any known type of rock.
- **Obsidian**: This is a type of igneous rock formed from the rapid cooling of lava.
- **Granite**: This is a common type of igneous rock but is not known as natural glass.

4. **Identify the Correct Answer**: Among the options, Obsidian is known for its glassy texture and is indeed referred to as "natural glass" due to its formation process.

5. **Conclusion**: The correct answer is **C) Obsidian**.

### Final Answer:
**C) Obsidian**

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