neplanarit

Neplanarit is a hypothetical mineral species used in speculative mineralogy and educational contexts to illustrate extreme‑pressure silicate behavior. It has not been observed in natural samples, and nothing about its existence has been confirmed by experimental synthesis under laboratory conditions.

Composition and structure: In proposed models, neplanarit has a framework consisting of interconnected SiO4 tetrahedra forming a three‑dimensional net with alternating layers of Na–Al–oxide complexes. A simplified empirical formula sometimes cited in discussions is Na2Al4Si8O22(OH)4, with partial Si in higher coordination at ultrahigh pressures. The crystal system is described as hexagonal or pseudo-hexagonal with a layered stacking that yields low birefringence in thin sections.

Formation and occurrence: Neplanarit is described as stabilizing under ultrahigh‑pressure conditions that exceed conventional subduction‑zone metamorphism, typically around 12–20 GPa in conceptual models. In such models, it could appear as inclusions within garnet and other high‑pressure assemblages, acting as an intermediate phase between pyroxenes and more compact silicates.

Properties: In speculative terms, neplanarit would have a Mohs hardness around 6.5, a specific gravity near 3.3, and refractive indices in the range nα ≈ 1.60, nβ ≈ 1.62, nγ ≈ 1.64. It would be colorless to pale yellow and exhibit poor to moderate cleavage along basal planes.

Etymology and usage: The name combines the hypothetical prefix “ne-” (new) with “planarit” to reflect its proposed planar silicate layers. In fiction and pedagogy, neplanarit serves as a teaching tool for phase transitions in deep Earth conditions. Related topics include high‑pressure minerals such as garnet, omphacite, and subduction‑zone metamorphism.