[Elamur Dictionary](https://md.dictionary.elamur.ai/free/en/) · [this page in HTML](https://dictionary.elamur.ai/free/en/english/corundum/)

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# corundum

noun (corundum — uncountable)

«corundum» in the English dictionary: everyday — its meanings, how the lessons use it, and examples, each with its tree on Mova.

## Everyday

Corundum is a very hard natural mineral made of aluminium oxide; rubies and sapphires are coloured kinds of corundum. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#m1)

### In the lessons

In science lessons about rocks and minerals, corundum scores 9 on the Mohs scale of hardness, second only to diamond (10). Because it is so hard, crushed corundum is used to make sandpaper and grinding tools (emery). Red corundum is ruby; blue and other colours are sapphire.

### Examples

- Rubies and sapphires are both corundum. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x1)
- Corundum is harder than almost any other mineral. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x2)
- On the Mohs scale, corundum is 9 and diamond is 10. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x3)
- Emery boards for nails contain corundum. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x4)
- Pure corundum has no colour. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x5)
- The museum showed a big red crystal of corundum. [tree →](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/#x6)

### Note

Uncountable. Pronounced «kuh-RUN-dum». A trap: ruby and sapphire are the same mineral, just different colours caused by tiny amounts of other metals.

## On Mova

- [Trees and pragmatics of «corundum» in the school dictionary](https://mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/): every meaning and example parsed by Mova, with its dependency tree and frames.
- [«corundum» in the school dictionary](https://mova.elamur.ai/free/en/dictionaries/school/w/corundum.html) on Mova free.