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

Options

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

Explanation

To solve the question "Which of the following types of rocks is also known as natural glass?", we will analyze the options provided and identify the correct answer step by step.

### Step 1: Understand the Question
The question asks us to identify a type of rock that is referred to as "natural glass."

### Step 2: Analyze the Options
We need to look at each option provided to determine which one fits the description of natural glass.

### Step 3: Evaluate Each Option
1. **First Option**: (Not specified in the transcript)
- The video mentions that this option is wrong and identifies it as a metamorphic rock. Therefore, it cannot be natural glass.

2. **Second Option: Obsidian**
- The video states that this is the correct answer. Obsidian is formed by the rapid cooling of lava, which prevents the formation of crystals, resulting in a smooth and shiny appearance. This is why it is referred to as natural glass.

3. **Third Option: Basalt**
- The video indicates that this option is wrong because basalt is an igneous rock. It does not have the properties of natural glass.

4. **Fourth Option: Greenite**
- The video also states that this option is wrong, as greenite is another type of igneous rock and does not qualify as natural glass.

### Step 4: Conclusion
After evaluating all the options, we conclude that the type of rock that is also known as natural glass is **Obsidian**.

### Final Answer
**Obsidian** is the type of rock that is also known as natural glass.

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