ludwigite

Ludwigite is a rare borate mineral with the chemical formula (Mg,Fe)2BO3F. It is characterized by its high refractive index and pleochroism, appearing green in one direction and yellowish-green in another. Ludwigite typically forms as acicular or prismatic crystals, often found in massive or granular aggregates. Its color can range from dark green to black, with paler varieties also existing.

This mineral is commonly found in skarns and contact metamorphic rocks, often associated with serpentine, magnetite, and dolomite. It can also occur in hydrothermal veins and pegmatites. Ludwigite was first discovered in the 19th century and is named after the German mineralogist Carl Friedrich Ludwig. Its occurrence is relatively localized, with notable deposits found in various parts of the world, including Austria, Russia, China, and the United States.

While not commercially significant for its mineral properties, ludwigite is of interest to mineral collectors and geologists due to its rarity and distinct crystallographic and optical characteristics. Its presence can provide clues about the metamorphic and geological conditions under which it formed.