For a good building stone, its specific gravity should be greater than
⚖️ Understanding Specific Gravity
Specific gravity is a key indicator of a stone's quality. It's a measure of how dense the stone is compared to water.
Specific Gravity (SG): The ratio of the density (mass per unit volume) of a substance to the density of a reference substance, which is usually water. Since water's density is 1 g/cm³, a stone with an SG of 2.7 is 2.7 times denser than water.
Why it matters: A higher specific gravity generally means the stone is denser, less porous, and stronger.
🔬 Detailed Analysis of the Values
D. Greater than 2.7
This is the correct answer. For a stone to be considered high quality, especially for structural purposes like foundations, dams, and retaining walls, it needs to be heavy and strong. A specific gravity of 2.7 or higher is a widely accepted benchmark for such stones. This indicates a dense, non-porous material with high strength.
A, B, and C (1.5, 1.7, 2.2)
These values represent stones that are progressively lighter and more porous. While some stones with an SG around 2.2 might be used for non-structural purposes, values as low as 1.5 or 1.7 indicate a very light, weak, and likely porous material that would be unsuitable for most building applications. Generally, any stone with a specific gravity below 2.4 is considered unsuitable for quality construction.
📊 Specific Gravity of Common Building Stones
While the general rule is to be greater than 2.7 for high quality, most good building stones fall within a range of 2.4 to 2.8.
| Stone Type | Typical Specific Gravity Range | Classification |
|---|---|---|
| Basalt | 2.8 - 3.0 | Very Heavy & Strong |
| Granite | 2.6 - 2.7 | Heavy & Strong |
| Slate | 2.6 - 2.8 | Heavy & Dense |
| Limestone | 2.3 - 2.7 | Medium to Heavy |
| Sandstone | 2.2 - 2.8 | Variable, can be light or heavy |
💡 Study Tips
- The 2.7 Benchmark: Remember 2.7 as the target number for a good, strong, heavy building stone.
- Higher is Better: For specific gravity, a higher number is almost always better as it implies greater strength and lower porosity.
- Connect SG to Use: High SG stones (like granite, basalt) are for heavy work (dams, retaining walls). Lighter SG stones are only suitable for non-load-bearing or decorative work.