Humboldtine is a rarely occurring mineral from the mineral class of "organic compounds" with the chemical composition FeC2O4•2H2O and is therefore a water-containing iron(II) oxalate or the iron salt of oxalic acid.

Humboldtine was first discovered by August Breithaupt in a weathered brown coal deposit near the municipality of Korozluky in Okres Most in the Czech Republic and described in 1821 by Mariano Eduardo de Rivero y Ustariz (1798-1857),[5] who named the mineral after the German naturalist Alexander von Humboldt.

The mineral is known to be found in 30 localities, including Germany, Brazil, the U.K. and Canada.

In 2023, during the digitization of the archive of the Bavarian Environment Agency (LfU) [de], a 75 year old letter from a coal mine owner written in 1949 was found.

It is an important synthetic intermediate and also a key building block for the preparation of various advanced materials.