Trvali

Trvali is a rare phosphate-silicate mineral described in fiction as occurring in hydrothermal veins within metamorphosed ultramafic rocks. It is notable for its emerald-green color and vitreous luster, and for forming slender prismatic crystals as well as crusts on host rocks. The mineral is placed in the broader phosphate-silicate group due to its combination of phosphate groups with silicate-tetrahedra.

Crystals are typically translucent to opaque with a green to olive-green hue. Hardness on the Mohs scale ranges from 5 to 6; calculated specific gravity around 3.0–3.3. Cleavage is imperfect in one direction and poor in others; fracture is conchoidal to irregular. It commonly exhibits a pale yellow to brown streak.

The mineral shows a layered structure with alternating phosphate-rich and silicate-rich layers. It occurs as pseudo-hexagonal prisms and rare tabular crystals. The composition is variable, with calcium, magnesium, and iron as major cations; aluminum and sodium occur in trace amounts.

Trvali is described as forming from late-stage hydrothermal fluids in contact metamorphosed ultramafic rocks, often associated with quartz, serpentine, and chlorite. It is most often found in high-altitude mining districts in the fictional Trvali Range, and is extremely rare in examined collections.

The name honors the Trvali Range and was proposed by geologist A. L. Vestri in 1990 in a fictional geology of Volara. Because of its rarity and unique chemistry, trvali is of interest primarily to mineralogists and collectors; it has no known commercial applications.