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