Hillityt

Hillityt is a fictional mineral introduced for educational and world-building purposes in geology and mineralogy. It is described as a phosphate-bearing silicate that forms under hydrothermal metamorphism of phosphate-rich rocks and is valued in fictional markets for its vivid blue-green color.

In most depictions, hillityt occurs in high-grade metamorphic terrains, especially alpine or subduction-zone complexes, where fluids interact with silicate and phosphate minerals. It is commonly associated with minerals such as apatite, quartz, and fluorite.

Physical properties commonly attributed to hillityt include a hardness of 5.5–6 on the Mohs scale, a blue to azure-green color, a white streak, and a vitreous to resinous luster. The mineral is described as transparent to translucent with a monoclinic crystal system and prismatic to tabular crystals; cleavage is usually imperfect. The estimated density is about 3.3–3.7 g/cm3.

The name hillityt derives from the fictional Hill region where it was said to be first observed, with the generic -yt suffix used in some mineral-name conventions.

In educational contexts, hillityt is used to illustrate mineral identification, classification, and the interpretation of paragenetic associations in metamorphic settings. In fiction and media, hillityt often appears as a coveted gemstone or as a plot element representing scarcity or purity.