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# Absolute or true specific gravity

Learn specific gravity, Absolute or true specific gravity, Table of specific gravity of soil constituent

## Specific gravity

Specific gravity is defined as the ratio of the weight of a given volume of soil solids at a given temperature to the weight of an equal volume of distilled water at that temperature, both weights being taken in air. In other words, it is the ratio of the unit weight of soil solids to that of water.

$G = \frac{\gamma_{s}}{\gamma_{w}}$

The Indian Standard specifies 27°C as the standard temperature for reporting the specific gravity. Some qualifying words like: true, absolute, apparent, bulk or mass, etc., are sometimes added to the term ‘specific gravity’. These qualifying words modify the sense of specific gravity as to whether it refers to soil particles or to soil mass. The soil solids have permeable and impermeable voids inside them, the permeable voids being capable of getting filled with water.

### Absolute or true specific gravity

Absolute or true specific gravity If all the internal voids of soil particles (permeable and impermeable) are excluded for determining the true volume of solids, the specific gravity obtained is called absolute or true specific gravity. The apparent or mass or bulk specific gravity Gm denotes the specific gravity of soil mass and is given by Unless otherwise specified, we shall denote the Specific Gravity G as the specific gravity of soil solids.

${G_{m} }= \frac{\gamma}{\gamma_{w}}$

## Specific gravity of soil constituents

Table gives the values of specific gravity of soil constituents
Soil constituentSpecific gravity
Aragonite2.94
Attapulgite

2.3
Augite3.2-3.4
Biotite3.0-3.1
Calcite2.72
Chlorite2.6-2.9
Dolomite2.85
Gypsum2.32
Halloysite2.55
Hematite5.2
Hornblende3.2-3.5
Illite2.6-2.86
Kaolinite2.64
K. feldspar2.54-2.587
Limonite3.8
Magnetite5.17
Montmorillonite2.75-2.78
Muscovite2.7-3.1
Na-Ca-Feldspar2.62-2.76
Orthoclase2.56
Pyrophylite2.84
Quartz2.65
Serpentine2.2-2.7
Talc2.7

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Absolute or true specific gravity
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Absolute or true specific gravity, Table of specific gravity of soil constituent
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