For a good building stone, its specific gravity should be greater than
Try it first: pick an option, then read the explanation.
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.