What is the nature of cell-walls in diatoms?

Explanation

**Step-by-Step Solution:**

1. **Identify the Composition of Diatom Cell Walls**: The cell walls of diatoms are primarily composed of silica. Silica is a strong and durable material.

2. **Structure of the Cell Walls**: The cell walls consist of two thin overlapping shells. These shells fit together in a manner that resembles a soap case, providing structural integrity.

3. **Durability of the Cell Walls**: Due to the presence of silica, the cell walls of diatoms are almost indestructible. This characteristic contributes to their resilience in various environments.

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