What's the plural form of grauwacke? Here's the word you're looking for.
Answer
The noun grauwacke can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be grauwacke.
However, in more specific contexts, the plural form can also be grauwackes e.g. in reference to various types of grauwackes
or a collection of grauwackes.