Which of the following possess more ability to resist fire?
🔥 Understanding Fire Resistance in Stones
Fire resistance is a crucial property for building materials. It refers to a stone's ability to withstand high temperatures without losing its structural integrity or breaking down chemically. The best fire-resistant stones are those that are dense and composed of minerals that are stable at high temperatures.
🔬 Detailed Analysis of the Options
A. Compact Sandstone
This is the correct answer. Sandstone is primarily composed of quartz (silica) grains cemented together. A compact, dense sandstone has excellent fire-resisting properties because its main component, quartz, has a very high melting point. The dense structure helps it maintain its integrity for a longer period when exposed to heat.
B. Quartz
While quartz is the fire-resistant mineral within sandstone, it is not typically used as a bulk building stone on its own. Furthermore, when pure quartz is subjected to intense and rapid heating (around 573°C), it can undergo a sudden expansion (a phenomenon called quartz inversion), which can cause it to crack or spall. Compact sandstone, being a composite material, manages this stress better. Therefore, as a building material, compact sandstone is considered the better fire-resistant option.
C. Red Marble
Marble is a metamorphic rock made of calcium carbonate (CaCO₃). It has very poor fire resistance. When heated, it undergoes a chemical process called calcination, where it breaks down into lime (calcium oxide) and carbon dioxide gas. This completely destroys the stone's strength and structure.
D. Shale
Shale is a soft, laminated (layered) sedimentary rock. It has poor structural strength and very low fire resistance. When heated, it easily splits along its layers and disintegrates, making it entirely unsuitable for fire-resistant construction.
📊 Summary: Fire Resistance of Different Stones
| Stone | Composition | Fire Resistance | Reason |
|---|---|---|---|
| Compact Sandstone | Mainly Quartz (Silica) | Good | High melting point of quartz and dense structure. |
| Marble | Calcium Carbonate | Poor | Decomposes (calcines) under heat. |
| Shale | Clay Minerals | Very Poor | Soft, laminated structure that splits easily. |
| Quartz (as a mineral) | Silica | High | High melting point, but can spall under thermal shock. |
💡 Study Tips
- Silica is Superior: Stones rich in silica (like sandstone) are generally good fire resistors. Stones rich in calcium (like marble and limestone) are poor fire resistors.
- Compact = Strong: The word "compact" is a key clue. A dense, compact structure is always better for resisting fire and other stresses.
- Marble Melts (Chemically): Remember that marble doesn't just get hot; it chemically changes into lime powder, losing all its strength.