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