Formula & Calculator
Rock/Mineral Density (Specific Gravity)
Compares a rock or mineral's density to that of water, a quick diagnostic property used in mineral identification.
Interpretation
SG = Density of Sample / Density of Water. The ratio of a mineral's density to the density of water. Used in mineral identification and ore body assessment.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| SG | Specific gravity | |
| Density of Sample | Sample density | g/cm3 |
| Density of Water | Reference water density (1 g/cm3) | g/cm3 |
What it means
Specific gravity (SG) is the ratio of the density of a substance to the density of water at a reference temperature (4°C). It is a dimensionless quantity. For minerals, SG is used in identification and classification. It also helps in estimating the volume of ore bodies from gravity surveys. Specific gravity is measured using a pycnometer or using hydrostatic weighing. Understanding SG is important in mineralogy, petrology, and geophysics for characterizing materials and for interpreting gravity anomalies.
Worked example
Specific Gravity – Two Detailed Examples
Real‑World| Parameter | Value |
|---|---|
| Sample Density (g/cm³) | 2.65 |
| Parameter | Value |
|---|---|
| Sample Density | 7.9 |
Common mistakes
- Specific gravity (SG): Density of sample / density of water – dimensionless.
- Density of sample: In kg/m³ or g/cm³.
- Density of water: Usually 1000 kg/m³ (at 4°C) – but depends on temperature.
- SG > 1: Most minerals have SG between 2 and 8.
- Porosity: Bulk density vs. grain density – SG of grains is different from bulk.
Applications
Rock/mineral density (specific gravity) is the ratio of the mass of a sample to the mass of an equal volume of water, providing a measure of mineral composition and porosity. This is used in mineral identification, ore reserve estimation, and geotechnical engineering. Geologists measure specific gravity to distinguish minerals, to assess rock quality, and to calculate the weight of rock masses for engineering projects. In mining, it is used to estimate tonnage of ore. By determining specific gravity, professionals can also infer porosity and fluid content. This property is essential for many aspects of geology, mining, and civil engineering.
- Mineral identification and characterisation
- Ore reserve estimation and mining calculations
- Geotechnical engineering – rock mass weight and stability
- Porosity and fluid saturation estimation
- Quality control in construction materials (aggregates)
Frequently Asked Questions
SG = Density of Sample / Density of Water. It is a dimensionless ratio comparing a mineral's density to that of water (at 4°C, ~1 g/cm³). It is a quick, diagnostic property.
- Quartz: 2.65
- Feldspar: 2.5–2.8
- Calcite: 2.71
- Pyrite: 5.0
- Gold: 19.3
Because its density is close to 1 g/cm³, making the numerical value of SG nearly equal to the density in g/cm³. It is a convenient standard.
Using a heavyliquid (e.g., bromoform, SG ~2.9) to separate minerals by flotation, or by the pycnometer method in the lab.
Since water density is ~1 g/cm³, SG ≈ density (in g/cm³) for rocks. For example, a rock with density 2.65 g/cm³ has SG 2.65.
It is one of several physical properties used to distinguish minerals. For example, galena (SG ~7.5) vs. quartz (SG ~2.65).
Bulk density includes the volume of pore spaces; specific gravity of a mineral refers to the solid material (no pores). For rocks, the bulk SG is lower if porosity is present.
Rocks with mafic minerals (e.g., basalt) have higher SG (2.8–3.0) than felsic rocks (e.g., granite, SG ~2.6).
Many minerals have overlapping SG ranges. It must be used in combination with other properties (hardness, colour, streak, etc.) for accurate identification.
It is used for gravity separation – heavy minerals are concentrated by their higher SG in processes like panning, jigging, or shaking tables.