Specific Gravity Calculator
Compare a rock or mineral's density with water, a quick diagnostic property for mineral identification. Solve for SG, sample density or water density, or measure SG by weighing in air and in water.
SG = ρsample / ρwaterSG = Wair / (Wair − Wwater)Step-by-step solution
Properties and likely matches
Measure SG by weighing (hydrostatic method)
Hang the sample from a thread on a balance, weigh it in air, then fully submerged in water without touching the sides. The sample must sink, be dense and non-porous, and have no trapped air bubbles. Water density comes from the main calculator above.
Where your sample sits
Mineral specific gravity
| Mineral | SG range |
|---|
Rock bulk density
| Rock | SG range |
|---|
Rock values are bulk densities and include pore space, so they vary more than mineral values. Your SG row is highlighted when it falls inside a range.
FAQ
What is specific gravity?
Specific gravity is the ratio of a material's density to the density of water, so it has no units. Quartz has an SG of about 2.65, meaning it is 2.65 times as dense as water.
How is SG different from density?
Density has units (g/cm³, kg/m³). In g/cm³ the two numbers are almost equal because water is about 1 g/cm³. In kg/m³ the density is about 1000 times the SG.
Why does water density matter?
Water is 0.99997 g/cm³ at 4 °C, 0.9982 at 20 °C and 0.9970 at 25 °C. The effect is small, but for precise work use the density at your measurement temperature.
How is SG used to identify minerals?
Most common rock-forming minerals fall between 2.5 and 3.5. Noticeably heavy samples (above about 4) often point to metallic minerals such as pyrite, galena or native metals. Use SG with hardness, streak and lustre, not on its own.
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)
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