Specific Gravity Calculator

Input dry weight and submerged weight to compute specific gravity. Compares results against known mineral densities to suggest possible identifications.

Analysis

Measurements

Result

How to Use

  1. 1
    Weigh the dry mineral specimen in air

    Place the specimen on an accurate balance and record its dry weight in grams. For precision, use a balance capable of resolving 0.01 g for specimens in the 5–50 g range. Ensure the specimen is dry—moisture in pores or cracks lowers apparent air weight and introduces systematic error.

  2. 2
    Weigh the specimen while fully submerged in water

    Suspend the specimen by a thin thread or wire from the balance arm so it hangs fully immersed in water without touching the container walls or bottom. Record the submerged weight. The weight loss equals the weight of the displaced water, which by Archimedes’ principle equals the specimen’s volume times the density of water (approximately 1.00 g/cm³ at 20°C).

  3. 3
    Calculate specific gravity and match to mineral candidates

    The tool computes SG = Wₐᴵᵣ / (Wₐᴵᵣ − Wₛᵤᵇ) automatically. Enter both weights and review the ranked mineral matches. Consider that specific gravity alone rarely identifies a mineral uniquely; use the result alongside hardness, streak, and luster to narrow candidates to a single species.

About

Specific gravity measurement exploits Archimedes’ principle—that a submerged body experiences a buoyant force equal to the weight of displaced fluid—to determine mineral density without measuring volume directly. The method dates at least to Archimedes himself (c. 287–212 BCE), who reportedly used water displacement to assess the purity of a gold crown, and was adapted for systematic mineralogy in the 18th and 19th centuries as balance precision improved.

Specific gravity provides a particularly sensitive compositional proxy because it integrates both atomic mass and crystal packing efficiency. Within a mineral series, SG increases predictably with substitution of heavier elements: in the olivine series, pure forsterite (Mg₂SiO₄) has SG 3.27 while pure fayalite (Fe₂SiO₄) has SG 4.39, allowing estimation of iron-magnesium ratio from SG measurements in well-characterized specimens. Similarly, in plagioclase feldspar, SG increases from 2.62 in albite (NaAlSi₃O₈) to 2.76 in anorthite (CaAl₂Si₂O₈), reflecting calcium’s greater mass compared to sodium.

In gemology, specific gravity is a standard property reported in gem identification reports. The Gemological Institute of America and other major laboratories use hydrostatic weighing, heavy liquid immersion, and electronic gem testers calibrated against SG reference standards to identify unknown stones. Combined with refractive index, absorption spectrum, and fluorescence, specific gravity allows definitive identification of virtually all gem materials.

FAQ

What is specific gravity and how does it differ from density?
Specific gravity is the dimensionless ratio of a material’s mass to the mass of an equal volume of water at a reference temperature (typically 4°C or 20°C, where water density is essentially 1.00 g/cm³). Because water density is approximately 1.00 g/cm³ at these reference conditions, specific gravity and density in g/cm³ are numerically equal, but SG has no units while density carries units of g/cm³ or kg/m³. In mineralogy, specific gravity is the preferred expression because it can be measured directly by hydrostatic weighing without knowing the specimen volume independently. For most practical purposes, a mineral with SG 5.0 has a density of 5.0 g/cm³ and is five times heavier than an equal volume of water.
What specific gravity range spans most common rock-forming minerals?
Most common silicate rock-forming minerals fall between SG 2.6 and SG 3.4. Quartz has SG 2.65, orthoclase feldspar 2.56, plagioclase feldspar 2.62–2.76 (increasing with calcium content), and muscovite mica 2.77–2.88. Mafic silicates are denser: olivine ranges from 3.27 (forsterite end-member) to 4.39 (fayalite end-member), and pyroxene augite averages about 3.3. Heavy minerals, typically defined as SG above 2.9, include garnet (3.5–4.3), zircon (4.6–4.7), rutile (4.2–4.3), and magnetite (5.2). Ore minerals in the sulfide and oxide groups have much higher specific gravities: galena 7.5, cassiterite 6.9–7.1, and native gold 15.5–19.3 depending on purity.
How accurate is hydrostatic weighing for porous or fine-grained specimens?
Hydrostatic weighing accuracy is reduced by specimen porosity, because water entering pores adds weight to the submerged measurement without contributing to the true mineral volume. Open-pored specimens like pumice, chalky calcite, or vesicular basalt must be saturated before weighing or sealed with a thin lacquer coating to prevent water infiltration; the coating weight must then be subtracted. Fine-grained, microcrystalline, or powdered specimens are difficult to measure by hydrostatic weighing and are better characterized by pycnometer (specific gravity bottle) methods that use precise measurement of displaced liquid volume. The Berman balance, designed specifically for gemology and mineralogy, uses a fixed-volume immersion vessel with a sensitivity sufficient to resolve SG differences of 0.01 in typical gem-sized specimens.
Why does gold have such a high specific gravity compared to other metals?
Gold’s high specific gravity (15.5–19.3 depending on purity) arises from its large atomic mass (197 amu), its face-centered cubic crystal structure that packs atoms efficiently, and relativistic electronic effects that cause gold’s 6s electrons to contract toward the nucleus, increasing electron density and consequently crystal density. The same relativistic effects also cause gold’s characteristic yellow color and chemical nobility. Platinum group metals—iridium (22.56), osmium (22.59), and platinum (21.45)—surpass gold in density because they combine large atomic masses with even more efficient atomic packing. These high densities make placer gold deposits detectable by gravity methods and explain why gold concentrates in stream sediment heavy mineral separates.
Can specific gravity distinguish natural from synthetic gemstones?
Specific gravity is a useful but not always definitive tool for distinguishing natural from synthetic gemstones, as well as from glass and simulants. Natural sapphire and synthetic sapphire (Verneuil or Czochralski method) are both corundum (Al₂O₃) with SG approximately 4.0–4.1, so SG cannot distinguish them. However, glass simulants for sapphire typically have SG 2.3–3.5, well below natural corundum. Synthetic moissanite (SiC, SG 3.21) has a distinctly lower SG than diamond (3.52), which aids discrimination alongside thermal conductivity testing. For treated stones, inclusions and growth structure revealed by gemological microscopy, combined with SG measurement, provide more reliable separation than either test alone.
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