Specific gravity of soil is:

Detailed Explanation

Specific gravity of soil solids depends on the mineral composition of the particles. For the great majority of natural soils — dominated by common rock-forming minerals such as quartz, feldspar, and clay minerals — the specific gravity of solids typically falls in the range of about 2.6 to 2.75, which is comfortably captured by the statement that G is more than 2.5 for most soils.

Specific gravity is not the same for all soil types (clays and sands can differ, and organic or highly weathered soils can have distinctly lower values), and it is measured directly using a density bottle or pycnometer (see Q23 and Q27), not a hydrometer (which is instead used to determine particle-size distribution of fine soils via sedimentation).

Key Concepts for Students

• Typical specific gravity for most inorganic soils: roughly 2.6-2.75, i.e., "more than 2.5" as a safe general statement.
• Specific gravity varies with mineral composition — it is not identical across all soil types (clays, sands, organic soils can all differ).
• Specific gravity is measured using a density bottle (fine soils, ~50 ml) or pycnometer (coarser soils, ~900 ml) — not a hydrometer, which serves a different purpose (grain-size analysis).
• Organic soils and some highly weathered residual soils can have specific gravities below 2.5, making them an exception to the general rule.