Mineralogy baseline: What is the standard specific gravity (Gs) value typically adopted for quartz in geotechnical and construction materials calculations?

Introduction / Context:
Specific gravity (Gs) is a key index property for minerals and soils. In geotechnical engineering, quartz is the dominant constituent of most sands and silty sands. Knowing the typical Gs of quartz helps in estimating unit weights, void ratios, and performing phase-relationship calculations when laboratory data are not yet available.

Given Data / Assumptions:

• Material considered: quartz (major constituent of silica sands).
• Standard temperature range for Gs determination is assumed.
• Engineering practice often uses a representative single value for preliminary work.

Concept / Approach:

Specific gravity Gs is the ratio of the density of solid particles to the density of water at a reference temperature. Most siliceous minerals, especially quartz, have a narrow Gs range near 2.65. This representative value is widely adopted for sands in preliminary analyses, such as computing dry unit weight and relative density when only index data are available.

Step-by-Step Solution:

Verification / Alternative check:

Textbooks and materials handbooks consistently list Gs for quartz around 2.65, with minor variation due to impurities or measurement temperature.

Why Other Options Are Wrong:

2.72 is closer to some feldspars; 2.85 and 2.90 are too high for quartz; 2.58 is low relative to accepted quartz values.

Common Pitfalls:

Confusing Gs of silica sands with lightweight or heavy minerals; using bulk specific gravity of aggregates (which includes voids) instead of particle specific gravity.

Final Answer:

2.65