chert.

A hard rock made largely of microscopic silica crystals.

Use it for

Words that belong together

• chert fragment
• chert bed

On the page

A chert fragment cut through the leather of his glove.

The chert bed stood out above the softer eroded layers.

Usage notes

Primary category: environment. Forms: Usually uncountable; plural cherts for distinct types or samples. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.