What is the density of alumina?

3,900 kg/m³ (3,700–3,980), or 3.90 g/cm³.

No. At 3,900 kg/m³ it is denser than water.

Alumina

Density of alumina

3,900 kg/m³ (3,700–3,980)

3.90 g/cm³ · 243.5 lb/ft³

The workhorse technical ceramic: hard at Mohs 9, an excellent electrical insulator, and cheap because it is made from the same bauxite feedstock as aluminum. Its stiffness of 370 GPa is nearly twice steel's, but it has no ductility whatsoever, so it fails suddenly from whatever flaw happens to be largest — which is why ceramic strength is quoted as a statistical distribution and why the tensile figures here are half the flexural numbers usually advertised. Corundum, ruby and sapphire are the same compound as single crystals.

Properties

Density: 3,900 kg/m³ (3,700–3,980) — 3.90 g/cm³
Melting point: 2,072 °C
Tensile strength: 200–300 MPa
Young's modulus: 370 GPa
Thermal conductivity: 30 W/(m·K)
Hardness: 9 Mohs
Thermal expansion: 8.1 µm/(m·K)
Floats in water: No
Magnetic: No

What it is used for

Grinding wheels and abrasives
Electronic substrates and insulators
Wear-resistant liners and pump seals
Ceramic body armour plate

How it compares

Water is 1,000 kg/m³. Anything with a shorter bar than water floats in it.

air 1.2 kg/m³

expanded polystyrene foam 20 kg/m³

rigid polyurethane foam 40 kg/m³

Water — the float line 1,000 kg/m³

alumina 3,900 kg/m³

tungsten 19,250 kg/m³

gold 19,300 kg/m³

platinum 21,450 kg/m³

Water is 1,000 kg/m³. Anything below that floats.
Material	Density	Relative to water
rigid polyurethane foam	40 kg/m³	0.04×
expanded polystyrene foam	20 kg/m³	0.02×
air	1.2 kg/m³	0.00×
alumina ←	3,900 kg/m³	3.90×
platinum	21,450 kg/m³	21.45×
gold	19,300 kg/m³	19.30×
tungsten	19,250 kg/m³	19.25×

Does it rust?

Alumina contains no iron, so it cannot rust. Whether it degrades depends on the material, not on oxidation.

Is it magnetic?

Alumina is not a metal and has no ferromagnetic response.

Common questions

What is the density of alumina?: 3,900 kg/m³ (3,700–3,980), or 3.90 g/cm³.
Does alumina float?: No. At 3,900 kg/m³ it is denser than water.
Is alumina magnetic?: Alumina is not a metal and has no ferromagnetic response.

Does alumina float? No
Concrete 2,400 kg/m³
Brick 1,900 kg/m³
Gypsum board (drywall) 700 kg/m³
Tungsten carbide 14,900 kg/m³
Reinforced concrete 2,500 kg/m³
Graphite 2,200 kg/m³
Porcelain 2,400 kg/m³
Plaster 1,100 kg/m³

Sources

Typical range compiled from manufacturer specifications — At One Place

How these figures are compiled and checked