Tunellite Crystal

What is Tunellite?

Tunellite is a relatively rare borate mineral known for its soft sheen and delicate, mica-like lustre. It is a delicate trace of ancient magma and vanished desert lakes, preserved in crystal form.

Under rare and precise conditions, Tunellite forms. Its formation begins during the final stages of volcanic eruptions, when boron becomes highly concentrated in mineral-rich geothermal fluids. Boron-rich waters must persist over long volcanic periods and collect in a closed, arid basin — a desert lakebed with no outlet, where water can only evaporate rather than drain away. The basin must be deep enough to build thick layers of mineral salts, with broad shallow margins and a deeper centre, and occasional natural flushing to remove non-borate salts while boron continues to concentrate. 

Containing strontium oxide (SrO) and water (H₂O) alongside boron (B₂O₃) — a combination found in only very few minerals — tunellite is both chemically unusual and geologically rare.