Limonite is the field term for a mixed assemblage of ferric oxyhydroxides, often containing nonferric silicate impurities. It is abundant on Earth's surface, possesses variable iron content, and is easily recognized by distinctive yellow and ochre hues. Limonite is a unique centerpiece for undergraduate chemistry laboratories because each sample represents a true unknown to faculty and students alike, and because limonite does not digest readily with common methods. Senior students were guided through a primary literature review to assess and establish an appropriate digestion method. Students then constructed the procedure for determining the iron content in limonite using atomic absorption spectroscopy. A final report, produced in the style of this "Journal," completed the start-to-finish process used by scientists, helping students learn how novel problems are solved in the laboratory. General chemistry students were provided with limonite extracts and used UV-vis spectroscopy to determine their iron contents, gaining proficiency in wet-lab, data collection, and analysis skills. Lab reports included an interdisciplinary discussion/interpretation of results from chemistry and geologic perspectives. The method used by students for digestion and iron extraction was validated using goethite and iron(III) oxide as standards (<3% error). The two spectrometric methods provided comparable results for the iron content in limonite. Despite challenging all students, these experiments were rated favorably in written evaluations, and students self-rated their learning gains as very high. Limonite experiments promote curiosity, discussion, and departure from laboratory exercises with predetermined results. Students become vested in analyzing a geologically important material that is inherently complex and heterogeneous.