# calcium carbonate

CEFR C1 · Noun

Source: https://englishreference.com/word/calcium-carbonate
Updated: 2026-08-05

## Definition

a white, solid substance found in rocks like limestone and marble, as well as in shells and bones. You often see it used in things like chalk, health supplements, or building materials.

For teachers: a chemical compound with the formula CaCO3, occurring naturally as limestone, marble, and chalk. It is a common substance in the shells of marine organisms and serves as a major component of agricultural lime and antacid medications.

## Examples

- Chalk is mostly made of calcium carbonate.
- The white cliffs are composed primarily of calcium carbonate formed from the skeletal remains of tiny sea creatures.
- In marine biology, the rising acidity of the oceans is a major concern because it prevents many organisms from effectively secreting calcium carbonate to build their shells.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.