Density of Diamond: 3,515 kg/m³ — Crystal Structure, Carbon Allotropes, and Gemology

Natural diamond density ranges from 3,500 to 3,530 kg/m³ depending on crystal type and trace impurities.

Type IIa (purest, colorless) is closest to the theoretical value of 3,515 kg/m³. Synthetic (lab-grown) diamond has the same density as natural diamond — identical crystal structure, identical density.

Carbon has one of the widest allotrope density ranges in nature. From airy activated carbon to ultra-hard diamond, pure carbon density spans nearly a factor of 10, driven entirely by bonding and spatial arrangement.

The density difference between graphite (2,090–2,230 kg/m³) and diamond (3,515 kg/m³) is approximately 57–68%. Both are pure carbon.

The entire difference arises from crystal structure: graphite's layered sp² sheets leave large inter-layer gaps, while diamond's sp³ tetrahedral network packs carbon atoms as tightly as the covalent bond length allows.

In diamond, each carbon atom forms four covalent bonds with its four nearest neighbours in a tetrahedral arrangement. This sp³ hybridisation creates a continuous three-dimensional network of strong, directional bonds. For the base mass-per-volume concept behind this comparison, see what is density.

The diamond cubic crystal structure is a face-centred cubic (FCC) lattice with an additional four atoms in the tetrahedral holes. This arrangement achieves an atomic packing fraction of approximately 34% — lower than FCC metals like copper (74%) or aluminium (74%). However, carbon atoms are extremely small (atomic radius 0.77 Å), so even at 34% packing efficiency, the mass per unit volume is high.

Graphite consists of flat hexagonal sheets (graphene layers) in which each carbon atom forms three sp² bonds within the plane. The fourth electron participates in a delocalised π-bond system above and below the sheet. This large inter-layer spacing is why graphite is so much less dense than diamond despite identical atomic composition.

Diamond forms deep in the Earth's mantle at pressures above approximately 4.5 GPa and temperatures above 1,000°C. At these extreme conditions, the graphite structure collapses and carbon atoms rearrange into the denser diamond structure. This is also the basis of high-pressure high-temperature (HPHT) synthetic diamond production: graphite is compressed to diamond conditions in a press, transforming it into diamond at the atomic level.

Specific gravity (SG) — the ratio of a gemstone's density to water's density — is one of the primary diagnostic properties used by gemologists to identify minerals. Diamond's SG of 3.52 is distinctive enough to help distinguish it from many simulants, though some natural gemstones have similar values.

Gemologists measure specific gravity using hydrostatic weighing — weighing the stone in air, then weighing it suspended in water, and applying Archimedes' principle: SG = weight in air / (weight in air − weight in water). For a loose diamond, this gives a reliable SG reading to ±0.01.

Cubic zirconia (SG 5.6–5.9) is immediately distinguishable from diamond (SG 3.52) by this method; moissanite (SG 3.22) requires additional optical testing because its density is closer to diamond's.

Laboratory-grown diamonds — whether produced by HPHT (high-pressure high-temperature) or CVD (chemical vapour deposition) methods — have the same crystal structure as natural diamonds. Carbon atoms are arranged in the same diamond cubic lattice with the same bond lengths and angles. The result is identical density: 3,515 kg/m³.

This is a critical distinction: lab-grown diamonds are chemically and physically identical to natural diamonds, while diamond simulants (cubic zirconia, moissanite) are different materials entirely. A density test cannot distinguish a lab-grown diamond from a natural diamond — both have SG 3.52. It can, however, immediately identify cubic zirconia (SG 5.6–5.9) as a non-diamond.

Industrial-grade synthetic diamond used in cutting tools, abrasives, and drill bits is produced in large quantities by HPHT and CVD processes. Its density is the same as gem-quality diamond (3,515 kg/m³), but it may contain more lattice defects and impurities that affect colour and optical properties without significantly changing density.

3,515 kg/m³ is extremely high for a non-metallic material, but only moderate-to-high across all materials. The comparison below gives scale.

Diamond is the densest known form of carbon and the densest common mineral, but it is less dense than all common metals. A diamond the size of a golf ball would weigh about 230 g — noticeably heavy for its size, but far lighter than an equivalent steel ball (410 g) or gold ball (1,010 g).

For broader comparisons across solids, liquids, and gases, open the density table.