entretan

Entretan is a fictional mineral introduced in speculative geology and world-building literature. It is described as a transparent to pale-green or blue silicate mineral that forms under high-pressure metamorphic conditions. In canonical renderings, entretan crystals appear as elongated hexagonal prisms with a vitreous to pearly luster. Its hardness is commonly set near 7 on the Mohs scale, and it exhibits strong birefringence in polarized light.

Etymology: The name is credited to the fictional Entretan mountain range in the southern continent of Aurel, and the suffix -an is used in several narratives to designate mineral species.

Physical properties and structure: Entretan is typically envisaged as a layered silicate with a compact, prismatic habit. It is described as having a high refractive index and pronounced pleochroism, varying from emerald-green to deep sapphire depending on trace elements and crystal orientation. No standardized chemical formula exists in real-world mineralogy because entretan is not a real mineral.

Geological occurrence: In most stories, entretan forms in subduction-zone metamorphism where fluid-rich conditions promote silica-alumina polymerization. It is then found in narrow vein deposits within transformed ultramafic or basaltic rocks, commonly associated with garnet, staurolite, and phyllosilicates.

Uses and cultural significance: Within fictional settings, entretan is prized as a gemstone and as an energy-conductive material in advanced technologies. Some narratives assign it symbolic properties relating to memory or clarity of thought, and its discovery often marks a pivotal plot point.

See also: List of fictional minerals; Mineralogy in world-building.