A reniform mass of fibrous crystals.
This is polished section of Goethite from near Socorro, New Mexico.
CHEMISTRY FeO(OH) Hydrogen iron oxide
CRYSTALLOGRAPHY Orthorhombic
CRYSTAL GROWTH AND HABITS Goethite crystals are prismatic, occasionally as thin flattened crystals. More commonly goethite occurs as aggregates of acicular crystals in divergent sprays, reniform or stalactitic masses or radially fibrous.
COLOR AND OTHER OPTICAL PROPERTIES Blackish brown to yellowish or reddish brown; opaque
HARDNESS 5 - 5.5
SPECIFIC GRAVITY 4.1 - 4.3
LUSTER Submetallic to silky or dull
STREAK brownish yellow
BREAKABILITY Goethite has a splintery fracture when it forms fibrous masses, otherwise is brittle with an uneven fracture.
OCCURRENCE Goethite is commonly found as a weathering product of iron bearing minerals. It may be directly deposited in hydrothermal solutions.
ASSOCIATED MINERALS Hematite, Pyrite, Siderite