sanidine

Sanidine is a specialized term used primarily in geology and mineralogy. It describes a specific variety of potassium feldspar that crystallizes at high temperatures, making it a key indicator for geologists identifying volcanic environments and the cooling history of igneous rocks.

As a technical mineralogical term, it is treated as an uncountable mass noun. It refers to the chemical substance or the mineral species as a whole rather than individual crystals, which would instead be referred to as "sanidine crystals."