The rock generally used for roofing, is
🏠 Properties of a Good Roofing Material
To be suitable for roofing, a material must have a specific set of properties. It needs to be:
- Impermeable: It must not allow water to pass through.
- Durable: It must resist weathering from sun, rain, and frost for many years.
- Lightweight: It should not place an excessive load on the roof structure.
- Workable: It must be possible to shape it into thin, uniform sheets or tiles.
🔬 Detailed Analysis of the Options
C. Slate
This is the correct answer. Slate is a metamorphic rock that is perfectly suited for roofing due to its unique properties.
- Formation: Slate is formed when a fine-grained sedimentary rock, like shale, is subjected to moderate heat and pressure.
- Key Property (Fissility): This process aligns all the clay minerals in the rock into parallel layers. This gives slate a property called "fissility" or "slaty cleavage," which means it can be easily and cleanly split into thin, strong, and flat sheets.
- Other Qualities: Slate is also very dense, making it waterproof, and it is highly durable, often lasting for over 100 years.
A. Granite
Granite is an igneous rock. While it is extremely durable and strong, it is not used for roofing because:
- It's too heavy: A roof made of granite tiles would require an incredibly strong and expensive support structure.
- It lacks fissility: Granite does not split into thin sheets. It must be cut with saws, which is a difficult and costly process.
B. Basalt
Basalt is another igneous (volcanic) rock. Like granite, it is very hard and durable, but it is also very dense and heavy. It does not have the property of fissility and cannot be split into thin tiles, making it unsuitable for roofing.
D. Pumice
Pumice is a volcanic rock that is famous for being extremely lightweight (it can even float on water). However, it is completely unsuitable for roofing because:
- It's highly porous: Pumice is full of gas bubbles, making it act like a sponge. It would absorb water instead of repelling it.
- It's not strong: It is a very soft and brittle rock that would not be durable enough for a roof.
📊 Quick Comparison for Roofing Suitability
| Rock | Key Property | Suitability for Roofing | Reason |
|---|---|---|---|
| Slate | Fissility (Splits into thin sheets) | Excellent | Waterproof, durable, and can be made into thin tiles. |
| Granite | Hard and Heavy | Poor | Too heavy; cannot be split into thin tiles. |
| Basalt | Hard and Dense | Poor | Too heavy; cannot be split into thin tiles. |
| Pumice | Porous and Light | Very Poor | Absorbs water; not strong or durable. |
💡 Study Tips
- Slate = Splits: The "S" and "L" in Slate can help you remember that it Slits easily into thin layers.
- Think of a Blackboard: Old-fashioned blackboards were made of slate. Imagine how flat and smooth they are—that's the property needed for roofing tiles.
- Roofing requires a "Sheet" material: Of the options, only slate can naturally be formed into the thin, sheet-like tiles needed for a roof.