Hylsyen

Hylsyen is a rare hydrous silicate mineral described as part of the phyllosilicate family. It was first described in the early 2010s from the Hylsyen area in a Nordic metamorphic belt, where it occurs as fine crystals within chlorite-rich rocks of greenschist facies. The mineral is typically found in microcrystalline form intergrown with other sheet silicates and alteration minerals.

The name Hylsyen derives from the locality where the type material was collected. The naming was proposed by the describing researchers and subsequently accepted by mineralogical nomenclature authorities, making Hylsyen a recognized entry in mineral databases.

In terms of composition and structure, Hylsyen is characterized by a sheet-like silicate framework with aluminum, magnesium, iron, and silicon as major elements, and hydroxyl groups accompanied by water in its structure. It crystallizes in a monoclinic system and exhibits a vitreous to pearly luster. Typical physical properties include a Mohs hardness around 5, pale green to gray color, and good cleavage on the {010} plane. Its density is reported in the low 3.0 g/cm3 range. The chemical formula is commonly represented as a hydrated aluminosilicate with trace components that reflect its formation environment.

Occurrence and paragenesis place Hylsyen in metamorphosed ultramafic and chlorite-bearing rocks formed under conditions of elevated fluids. It is often found in association with chlorite, serpentine, magnetite, and other phyllosilicates. Hylsyen is of interest primarily to mineralogists and petrologists as an indicator mineral for fluid-assisted metamorphism and subduction-zone processes, rather than as an ore mineral.

See also: list of minerals, phyllosilicates, metamorphic rocks.