---
title: "Slate — density, melting point and properties"
description: "Slate has a density of 2,750 kg/m³ (2,650–2,900). Melting point, strength, conductivity, what it is used for, and whether it floats, rusts or is magnetic."
url: https://atoneplace.net/material/slate/
site: "At One Place"
---

# Slate

**Density of slate: 2,750 kg/m³ (2,650–2,900)**

2.75 g/cm³ · 171.7 lb/ft³

Its defining property is cleavage: metamorphism aligned the clay minerals so the rock splits into sheets a few millimetres thick, which is what makes a roofing slate possible and is nothing to do with the original sedimentary bedding. It is essentially waterproof, with under 0.4% absorption, so a good slate roof lasts over a century. Snooker tables use slate beds because a 25 mm slab can be ground flat to a fraction of a millimetre and will not warp with humidity.

## Properties

- **Density:** 2,750 kg/m³ (2,650–2,900) — 2.75 g/cm³
- **Tensile strength:** 10–30 MPa
- **Young's modulus:** 60 GPa
- **Thermal conductivity:** 2 W/(m·K)
- **Hardness:** 3.5 Mohs
- **Thermal expansion:** 10 µm/(m·K)
- **Floats in water:** No
- **Magnetic:** No

## What it is used for

- Roofing tiles
- Floor tiles and worktops
- Snooker and billiard table beds
- Electrical switchboards (historically)

## 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
- slate: 2,750 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× |
| slate ← | 2,750 kg/m³ | 2.75× |
| platinum | 21,450 kg/m³ | 21.45× |
| gold | 19,300 kg/m³ | 19.30× |
| tungsten | 19,250 kg/m³ | 19.25× |

## Does it rust?

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

## Is it magnetic?

Slate is not a metal and has no ferromagnetic response.

## Common questions

### What is the density of slate?

2,750 kg/m³ (2,650–2,900), or 2.75 g/cm³.

### Does slate float?

No. At 2,750 kg/m³ it is denser than water.

### Is slate magnetic?

Slate is not a metal and has no ferromagnetic response.

## Related pages

- [Does slate float?](https://atoneplace.net/does-it-float/slate/)
- [Diamond](https://atoneplace.net/material/diamond/)
- [Granite](https://atoneplace.net/material/granite/)
- [Marble](https://atoneplace.net/material/marble/)
- [Quartz](https://atoneplace.net/material/quartz/)
- [Limestone](https://atoneplace.net/material/limestone/)
- [Sandstone](https://atoneplace.net/material/sandstone/)

## Sources

- United States Geological Survey — USGS (https://www.usgs.gov/) [Public domain (US Government)]