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