Chert (noun)

A very fine-grained, hard, and dense sedimentary rock, typically light gray or white, that is composed mainly of silica and is found in many parts of the world.

Origin:

From old english cærst, from proto-germanic *krastaz (rock).

Examples:

1. Chert is a type of rock that is very hard and dense.
2. Chert is commonly used for making tools and weapons.
3. Chert is a sedimentary rock that is rich in silica.
4. Chert is a good rock for making knives and arrowheads.
5. Chert is formed by the precipitation of silica from hot springs or geysers.