Proto-Slavic *tvьrdъ

→ English quartz (mention)

→ Belarusian цвёрды (inherited)

→ Bulgarian твърд (inherited)

→ Czech tvrdý (inherited)

→ Czech tvrz (mention)

→ Old Church Slavonic тврьдъ (inherited)

→ Danish kvarts (derived)

→ German Quarz (derived)

→ Lower Sorbian twardy (inherited)

→ Spanish cuarzo (derived)

→ Upper Sorbian twjerdy (inherited)

→ Lithuanian tvirtas (link)

→ Macedonian тврд (inherited)

→ Dutch kwarts (derived)

→ Polish twardy (inherited)

→ Russian твёрдый (inherited)

→ Serbo-Croatian tvrd (inherited)

→ Serbo-Croatian тврд (inherited)

→ Slovene trd (inherited)

→ Ukrainian твердий (inherited)

→ Old Armenian թրծեմ (mention)