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