vastusummia

Vastusummia is a fictional mineral described in speculative geology and science fiction. It is said to form under ultrahigh-pressure conditions in subduction-zone rocks and is notable for a deep indigo to violet color and a high, adamantine-like luster.

Etymology and scope: The name combines Latin roots meaning vast and summit, reflecting a supposed occurrence at great depths within tectonic interfaces. In its fictional context, vastusummia is treated as a rare, newly identified silicate mineral rather than a well-established species.

Physical properties: Reported crystal habit is prismatic to tabular, with crystals ranging from a few millimeters to several centimeters in size in the stories where it appears. It is described as hexagonal to potentially trigonal in crystal system, with Mohs hardness around 7.5 and a specific gravity near 4.9. Optical properties are often depicted as high refractive index and strong violet pleochroism, contributing to its striking appearance in imagined samples.

Composition and formation: vastusummia is described as a silicate-dominant mineral with trace transition metals, particularly vanadium and aluminum, imparting its characteristic color. It is said to crystallize from silica-rich fluids during ultrahigh-pressure metamorphism of basaltic rocks, in association with other high-pressure minerals such as coesite and garnet in speculative subduction-zone assemblages.

Occurrence and significance: In fictional accounts, vastusummia has been found in a small number of samples from an imagined ultrahigh-pressure terrane, often linked to a hypothetical Borealis Subduction Zone. It is discussed primarily as a subject of theoretical mineral physics and as a plot device in fiction, rather than as a recognized mineral species. No current commercial uses are described; any practical interest lies in speculative studies of mineral stability at extreme conditions.