Spindlile

Spindlile is a rare aluminosilicate mineral noted for its elongated, spindle-shaped crystals. It was first described in 1999 by mineralogists studying metamorphic rocks of the Spindle Range in the southern Cordillera. The name derives from its distinctive spindle-like habit observed in hand specimens and thin sections.

Spindlile crystallizes in the monoclinic system and commonly forms prismatic crystals up to several centimeters long. It is typically colorless to pale blue-green, gray, or yellowish, with a white streak. The mineral has a vitreous luster, a hardness of about 6 on the Mohs scale, and a specific gravity around 3.2. It is transparent to translucent and shows a subtle pleochroism in some crystals.

Chemically, spindlile is an aluminosilicate framework that incorporates aluminum and silicon with light alkalis and calcium, along with trace amounts of titanium and chromium that influence color. Optical properties are biaxial (+), with refractive indices approximately nα ≈ 1.65, nβ ≈ 1.67, and nγ ≈ 1.69, and a birefringence near 0.02. Cleavage is imperfect, and habit remains the most diagnostic feature in hand samples.

Occurrence and formation: Spindlile is found in high-temperature hydrothermal veins and contact metamorphic zones within aluminous rocks. It commonly associates with minerals such as spinel, quartz, muscovite, and cordierite. It forms through metasomatic alteration and metamorphic recrystallization under moderate to high grade conditions.

Etymology and usage: The term spindlile is used in mineralogical literature to designate this mineral. While it has limited commercial value, it is of interest to researchers as a tracer of metamorphic conditions and crystal-chemical behavior in silicate systems.