Specific Gravity (Mineral) Calculator
Density of a mineral compared to water.
Formula first
Overview
Specific gravity is a dimensionless ratio that compares the density of a mineral to the density of pure water at 4°C. It serves as a primary diagnostic tool in mineralogy, determined by weighing a sample in air and then measuring its apparent weight when submerged in water to calculate the volume based on buoyancy.
Symbols
Variables
SG = Specific Gravity, = Weight in Air, = Weight in Water
Apply it well
When To Use
When to use: This formula is applied when identifying a high-purity mineral specimen where the chemical identity is unknown but physical measurements can be taken. It assumes the mineral is non-porous, does not dissolve in water, and that the sample is large enough to minimize scale error.
Why it matters: It allows geologists to differentiate between minerals that appear identical, such as distinguishing pyrite from gold, without destructive testing. In industrial mining, specific gravity is essential for gravity separation techniques used to refine ores.
Avoid these traps
Common Mistakes
- Adding units to Specific Gravity (it is dimensionless).
- Failing to account for porous rocks absorbing water during the test.
One free problem
Practice Problem
A mineral specimen weighs 50.0 grams in air and 30.0 grams when fully submerged in water. Calculate the specific gravity of the specimen.
Solve for: SG
Hint: The denominator of the formula represents the buoyancy force, or the weight of the water displaced.
The full worked solution stays in the interactive walkthrough.
References
Sources
- Manual of Mineralogy (Klein and Hurlbut)
- Britannica: Specific gravity
- Wikipedia: Specific gravity
- Dana's Manual of Mineralogy
- IUPAC Gold Book: Relative density (specific gravity)
- Manual of Mineral Science (23rd ed.) by Cornelis Klein and Barbara Dutrow
- Earth Materials: Components of a Dynamic Earth by Dexter Perkins and Kevin R. Henke
- A-Level Geology — Mineralogy