Obeliskit

Obeliskit is a fictional mineral used in geology education and speculative mineralogy to illustrate crystal habit, composition, and classification. It is defined as a silicate mineral that forms slender, obelisk-shaped crystals and is commonly described in teaching models to demonstrate crystal habit and mineral nomenclature.

Composition and structure: Obeliskit is depicted as a calcium- and aluminum-rich silicate framework with traces of alkali metals and rare earth elements. In educational representations, its hypothetical chemical formula is given as (Ca,Na)2(Mg,Fe)3Al2Si6O20, with variation in stoichiometry depending on impurities. The mineral is described as transparent to translucent with a vitreous luster, and it ranges in color from colorless to pale yellow. Mohs hardness is assigned around 6, and a typical specific gravity is placed in the 3.2–3.6 range.

Crystal system and habit: In the illustrative model, obeliskit crystallizes in a hexagonal system and tends to form elongated prismatic crystals that resemble small obelisks. These crystals are often depicted in radiating aggregates or solitary tabular prisms, contributing to their distinctive habit.

Occurrence and formation: In the fictional scenario, obeliskit is reported from pegmatitic pockets and contact metamorphic zones within the Obelisk Range of northern Terradyne. It is described as forming under moderate-grade metamorphism, commonly associated with zeolite or garnet assemblages, and occasionally found in hydrothermal veins.

Usage and significance: Within teaching contexts, obeliskit serves as a case study for crystal habit, fracture patterns, and mineral naming conventions. It is not known to occur in nature outside of fictional or illustrative scenarios, and no commercial applications are associated with it.