Question

A halide with octahedral cleavage can scratch calcite and can be scratched by quartz. Identify the halide.

• A. Sylvite
• B. Fluorite
• C. Apatite
• D. Halite

Hint:

Fluorite is known for its octahedral cleavage and a hardness of 4, which allows it to scratch calcite but be scratched by quartz.

Answer 1

The Correct Option is B

Step 1: Understanding the properties.
To identify the halide, we must focus on two properties: - Cleavage type: Octahedral cleavage refers to a crystal that splits along planes with 8 faces, which is typical of halite and fluorite.
- Hardness: The ability to scratch calcite (hardness of 3) and be scratched by quartz (hardness of 7) helps narrow down the possibilities. The hardness of fluorite is 4, making it capable of scratching calcite but not quartz.

Step 2: Analyzing each option.
- (A) Sylvite: Sylvite has cubic cleavage and a hardness of 2. It can scratch calcite, but it is too soft to be scratched by quartz.
- (B) Fluorite: Fluorite has octahedral cleavage and a hardness of 4, which fits the description of being able to scratch calcite and being scratched by quartz. This makes it the correct choice.
- (C) Apatite: Apatite has a hardness of 5 and typically exhibits poor cleavage, not octahedral. It is also not scratched by quartz.
- (D) Halite: Halite has cubic cleavage and a hardness of 2, which means it can scratch calcite but not be scratched by quartz.

Step 3: Conclusion.
Fluorite is the halide that has octahedral cleavage, can scratch calcite, and can be scratched by quartz. Hence, the correct answer is (B).
\[ \boxed{\text{Fluorite}} \]