phonolite

This term is used exclusively within the specialized fields of geology and petrology. It describes a specific type of igneous rock characterized by its high feldspar content and a unique physical property: the ability to emit a clear, metallic ring when struck with a hard object. This acoustic quality is the primary diagnostic feature that distinguishes it from other similar volcanic rocks.

As a technical classification of mineral matter, the word is treated as an uncountable mass noun. It refers to the material substance itself rather than individual stones or specimens, which would typically be referred to as "samples of phonolite" or "phonolite rocks."