Inhibiitorite

Inhibiitorite is a rare phyllosilicate mineral typically occurring as dark-gray to black foliated or fibrous masses. It is composed primarily of iron, magnesium, aluminum, silicon and hydroxyl groups, and it commonly forms fine-grained aggregates rather than well-formed crystals. The mineral is named for its characteristic tendency to form protective surface coatings that inhibit oxidative weathering of sulfide minerals.

Physical properties include a soft to moderate Mohs hardness (approximately 2.5–3.5), a submetallic to dull luster, and a dark brown to black streak. Inhibiitorite commonly shows perfect cleavage parallel to the layering and has a relatively low specific gravity (around 2.6–2.9). It typically crystallizes in a monoclinic system and is often associated with other alteration minerals such as chlorite, serpentine and iron oxides.

Inhibiitorite is most often encountered in hydrothermally altered mafic to ultramafic host rocks and in the oxidative rinds of sulfide-bearing ores, where it forms during low-temperature aqueous alteration. Its ability to form adherent, less-permeable coatings on sulfide surfaces has attracted interest in environmental mineralogy and corrosion studies, particularly for its potential to limit acid generation from mine wastes.

Occurrences are generally localized and of limited economic importance; specimens are mainly of interest to mineral collectors and researchers studying weathering processes and passive treatment strategies for sulfide-rich materials.