Question

Given below are two statements:
Statement (I): 2:1 layer silicates consist of two tetrahedral sheets bound to either side of an octahedral sheet.
Statement (II): Two tetrahedral sheets of 2:1 layer silicates is bound to one side of an octahedral sheet in 2:1 layer silicates.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are correct.
• B. Both Statement (I) and Statement (II) are incorrect.
• C. Statement (I) is correct but Statement (II) is incorrect.
• D. Statement (I) is incorrect but Statement (II) is correct.

Hint:

Remember the layer ratios:
- 1:1 Minerals (e.g., Kaolinite) $\rightarrow$ 1 tetrahedral sheet + 1 octahedral sheet.
- 2:1 Minerals (e.g., Montmorillonite) $\rightarrow$ 2 tetrahedral sheets sandwiching 1 octahedral sheet.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Phyllosilicate clay minerals are classified based on the ratio and arrangement of basic structural units: silicon-oxygen tetrahedra and aluminum/magnesium octahedra.

Step 2: Detailed Explanation:
- Statement (I) is correct: In 2:1 layer silicates (such as smectite, illite, and vermiculite), the basic structural unit consists of one central octahedral sheet sandwiched between two silica tetrahedral sheets (one bound on either side).
- Statement (II) is incorrect: The two tetrahedral sheets are located on opposite sides of the central octahedral sheet to balance the structural charge and form a symmetrical sandwich-like layer. Having both tetrahedral sheets bound to only one side of the octahedral sheet is structurally impossible for a 2:1 mineral.

Step 3: Final Answer:
Statement (I) is correct but Statement (II) is incorrect.