What is Vonsenite?
Vonsenite is an iron borate of the ludwigite-vonsenite series, found in magnesium- and iron-rich metamorphic rocks and valued for its dark compact crystals.
Mineralogy and structure
Reference formula: Fe3BO5. Vonsenite is orthorhombic with the ideal formula Fe2+2Fe3+BO5. COD 1511155 is a labelled natural representative because the ludwigite-vonsenite series permits Fe-Mg substitution. Vonsenite is classified with borates and has orthorhombic crystal symmetry. Typical hardness is 5.5–6 on the Mohs scale and specific gravity is approximately 4.7–4.9.
Colour, lustre and habit
Typical colours include black, brown-black, bronze, grey. The usual prismatic, granular, massive habit and sub-metallic, metallic, dull lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Vonsenite forms in or is associated with contact-metamorphic skarns, boron-rich iron formations and magnesium-rich metamorphic rocks. Important documented localities include the United States, Russia, Italy, Austria, Sweden and other skarn localities.
Dark iron borate from a skarn
Vonsenite is a specialist collector mineral whose value is tied to the ludwigite-vonsenite series and the metamorphic environment that produced it. Form, association and chemistry matter more than polish.
Collecting and care
Protect from impact and abrasion, avoid dust-producing work, and retain the skarn association and analytical information.
