This is the 4506th most frequent Polish word.
kopalniach
"Mine" (plural, locative case) - refers to places where minerals are extracted.
The word 'kopalniach' refers to the plural locative case, meaning 'mines' in a context describing a location or setting where actions occur.
Pracowałem kiedyś w kopalniach węgla kamiennego.
I once worked in coal mines.
Here, 'kopalniach' indicates a locative sense to describe where the minerals are found.
W kopalniach można znaleźć różnorodne minerały.
Various minerals can be found in mines.
This usage of 'kopalniach' emphasizes the location of the challenging work conditions, again using the plural locative case of 'kopalnia'.