Goethite
Image: <bdi><a href="https://www.wikidata.org/wiki/Q56247090" class="extiw" title="d:Q56247090"><span title="mineral collector and dealer">Robert M. Lavinsky</span></a></bdi> (CC BY-SA 3.0)
Mineral NameGoethite
Chemical FormulaFeO(OH)
Mohs Hardness5
Crystal Systemorthorhombic
Streak Coloryellowish-brown
Cleavageperfect on {010}
Fractureuneven
Specific Gravity3.3
Colorsdark brown, black, yellowish-brown, iridescent (rainbow, green, pink, purple)
Transparencyopaque
Type LocalityCoon Creek Mine (York Mine), Shady, Polk County, Arkansas, USA
Mineral GroupOxides
Usesiron ore, pigment, collector's mineral
Associated Mineralshematite, limonite, quartz, calcite
Raritycommon
Description
This specimen features a striking botryoidal habit with a vibrant iridescent tarnish, displaying a spectrum of greens, pinks, purples, and yellows over a dark, submetallic surface.
Geological Context
Goethite is a common secondary mineral formed by the weathering of iron-rich minerals in oxidizing environments, often found in hydrothermal deposits, bogs, and as a major component of limonite.
