propellerites

Propellerites are a rare mineral distinguished by a propeller-shaped crystal habit. Crystals typically form two to four blades radiating from a central axis, yielding a cross-section reminiscent of a propeller. The mineral presents a vitreous to pearly luster, a Mohs hardness of about 5 to 6, and a relatively low to moderate density. Crystal blades are often prismatic or tabular and can twine or intergrow, producing complex aggregates. Colour ranges from pale gray to olive green, sometimes with iridescent tarnish on exposed faces.

Propellerites crystallize in hydrothermal environments where silica- and aluminosilicate-bearing fluids circulate through volcanic and metamorphic rocks. Growth occurs as conditions shift, favoring rapid anisotropic accretion along specific crystallographic directions. The mineral is commonly associated with quartz, calcite, chlorite, microcline, and other secondary silicates.

Propellerites have been reported from several regions worldwide, including European, North American, and Asian hydrothermal belts. The type locality is described from a setting influenced by sedimentary and volcanic activity, and subsequent finds have shown a range of blade counts and color varieties. Specimens are typically small to medium in size, with well-formed crystals valued by collectors and researchers.

Taxonomically, propellerites are placed within a broader silicate mineral group characterized by distinctive anisotropic growth forms. The name derives from the characteristic blade-like habit that resembles a propeller. They are primarily of interest to mineral collectors and to researchers studying crystal growth in hydrothermal systems; no major industrial applications are currently known.