berüül

Berüül is a fictional mineral described in speculative geology and science fiction literature. It is notable for its translucent to transparent body and a vivid iridescent sheen that shifts from blue to green under different lighting. The mineral commonly shows strong pleochroism and a faint halo of luminescence when exposed to ultraviolet light.

The name berüül was coined in the mid-22nd century by researchers working in the Hyrren Basin, and is said to derive from a local term meaning light-weaver. In-world, berüül is treated as a rare, highly valued mineral with distinctive aesthetic properties.

Berüül typically occurs as prismatic to tabular crystals, though large masses are uncommon. Mohs hardness is described as 5–6 and specific gravity around 3.2. It is commonly described as a silicate mineral with a layered microstructure that contributes to its optical effects. Refractive index ranges from about 1.60 to 1.75, and it exhibits birefringence with moderate pleochroism.

Berüül forms in late-stage granitic pegmatites and hydrothermal veins, often associated with quartz, feldspar, and topaz. It is relatively scarce, with the largest deposits reported in a few continental shield regions in speculative geologies.

In fiction, berüül is prized as a gemstone for jewelry and ornamental carvings, and is studied for potential photonic and luminescent applications. Synthetically produced berüül variants appear in trade as lab-grown simulants. Environmental and ethical considerations mirror those of other rare minerals in the setting.