Why the test works
Specific gravity compares a material’s density with water. In a hydrostatic test, the difference between dry and submerged weight corresponds to the displaced water volume.
The method works best on a single compact specimen. Pores, attached matrix, multiple minerals, trapped air, absorbent material, and water-soluble minerals can shift the result substantially.
How to perform the test
- 1
Screen the specimen
Do not immerse porous, crumbly, water-soluble, reactive, valuable, treated, contaminated, or unknown hazardous material.
- 2
Measure dry mass
Tare the scale, weigh the dry specimen, and record the units and precision.
- 3
Prepare suspension
Tare the scale with the water container and empty sling arranged exactly as they will be used.
- 4
Measure while submerged
Suspend the specimen completely under water without touching the bottom or sides. Remove visible bubbles and record the stable reading.
- 5
Calculate and repeat
Divide dry mass by dry mass minus submerged apparent mass. Repeat the measurement; disagreement signals bubbles, contact, absorption, or insufficient scale precision.
How to read the result
Near 2.6 to 2.8
Common among quartz, feldspar, calcite, and many ordinary silicate or carbonate materials; the value alone is not distinctive.
Near 4 to 5
Noticeably dense minerals such as barite, some iron oxides, and several sulfides become plausible; use streak, hardness, cleavage, and safety context.
Above roughly 7
Very dense native metals or lead-rich minerals may be possible, but mixtures and measurement error must be excluded.
Repeated values differ substantially
The specimen or setup is unsuitable: check bubbles, water absorption, contact, thread tare, scale precision, and mixed composition.
Examples from the LithoMap guide library
Quartz
Specific gravity about 2.65; ordinary heft for a common light-colored mineral.
Barite
Unusually heavy for a pale nonmetallic mineral; around 4.5.
Galena
Very dense, commonly around 7.5, with lead-safe handling required.
Gold
Exceptionally dense when pure, but host rock, pores, and other metals lower bulk measurements.
Common mistakes
- Letting the specimen touch the cup
- Leaving bubbles on rough surfaces
- Using a scale too coarse for a small sample
- Ignoring absorbent thread or failing to tare the suspension
- Testing porous, mixed, or water-sensitive material as though it were a single mineral
Test safely
- Do not immerse unknown mine waste, lead-bearing dust, soluble salts, reactive material, radioactive candidates, or specimens that could contaminate the water.
- Treat the used water and container as contaminated when the specimen has any hazard uncertainty; do not use food vessels.
- Wash hands and work surfaces after handling dense ore minerals.
- Density supports identification but does not determine purity, metal content, value, or safe handling.
This method supports preliminary field identification. It is not laboratory confirmation, appraisal, hazard clearance, proof of origin, or permission to collect or alter a specimen.
Frequently asked questions
Is heft enough to identify a mineral?
No. Heft can flag an unusually light or heavy specimen, but size and shape bias perception. A measurement plus independent properties is much stronger.
Why does a porous rock give a poor result?
Open pores trap air and then absorb water, so the displaced volume and submerged reading change during the test.
Are density and specific gravity identical?
Density has units of mass per volume. Specific gravity is a dimensionless ratio to water. Their numerical values can look similar in common metric units, but they are different quantities.
Authoritative sources
LithoMap wrote this guide in original language using the physical-property standards and safety information supported by these sources.
- Minerals and their physical properties U.S. National Park Service
- Natural Gemstones: Mineral Gemstones U.S. Geological Survey
- Kansas Rocks and Minerals: Mineral Identification Kansas Geological Survey
Editorial review: September 18, 2026.