corundum

/kəˈrʌndəm/ (bre, ipa) · /kəˈrʌndəm/ (ame, ipa) · /kə-ˈrən-dəm/ (ame, mw)

corundum — noun

1. a very hard mineral made of aluminum oxide. Pure corundum has no colour, but tin

1.名詞C2
釋義

a very hard mineral made of aluminum oxide. Pure corundum has no colour, but tiny amounts of other elements create the red of rubies and the blue of sapphires. It is also made artificially and used on tools for grinding and polishing hard surfaces.

例句

Kim's engagement ring has a blue sapphire, which is a gemstone formed from the mineral corundum.

formed from the mineral — passive + source material

Mei used a grinding wheel coated with synthetic corundum to polish the marble countertop.

coated with synthetic corundum — passive describing tool surface

同義詞
  • alumina

    Alumina (aluminum oxide) is the chemical compound that corundum is made of; it is not a synonym for the natural mineral

  • emery

    Emery is a dark granular mixture that contains corundum and is used as an abrasive; it is coarser and less pure

文法句型

corundum (uncountable) — the mineral in general

corundum crystal / corundum stone (countable) — individual specimens

用法筆記

Corundum is uncountable when referring to the mineral in general (e.g., 'a layer of corundum'). It may appear as a countable noun in specialised contexts that refer to individual crystals or stones ('corundum crystals', 'coloured corundums').

常見錯誤

❌Rubies and sapphires are completely different minerals.
✅Rubies and sapphires are both forms of the mineral corundum.
💡They are colour varieties of the same mineral, not different minerals.