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# corundum

«corundum» in Mova's school dictionary: **a very hard natural mineral made of aluminium oxide…** — its meaning for a pupil, its sense in the lessons and examples, with 3 sentences of Mova's corpora that use it.

### part of speech

noun (corundum — uncountable)

### meaning for a pupil

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

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

### In the corpora

- [Rubies and sapphires are one mineral, corundum, and a pinch of another element decides the colour.](https://md.mova.elamur.ai/free/en/corpora/school/geography/51-gemstones-and-precious-metals/5/)
- [Rubies and sapphires are the same mineral, corundum; red corundum is ruby, and other colours are sapphire.](https://md.mova.elamur.ai/free/en/corpora/school/geography/51-gemstones-and-precious-metals/12/)
- [Tiny traces of other elements, such as chromium in ruby, give corundum its colour.](https://md.mova.elamur.ai/free/en/corpora/school/geography/51-gemstones-and-precious-metals/13/)

### Trees and pragmatics

[Every meaning and example of «corundum» parsed by Mova](https://md.mova.elamur.ai/free/en/corpora/dictionaries/school/C/corundum/), each sentence with its dependency tree and frames.