goethiite

Goehthite is a mineral composed of iron(III) oxide-hydroxide, with the chemical formula FeO(OH). It is a common component of rust and is found in soils and sedimentary rocks. Goethite crystallizes in the orthorhombic crystal system and is typically found as prismatic or acicular crystals, often in radiating aggregates or as earthy masses. It can also occur in stalactitic or botryoidal forms.

The color of goethite varies from yellow-brown to reddish-brown, depending on its purity and the presence of other elements. Its streak is typically yellowish-brown. Goethite is relatively soft, with a Mohs hardness of 5 to 5.5, and has a specific gravity of around 4.2 to 4.4. It is insoluble in water but soluble in strong acids.

Goethite forms through the weathering of iron-bearing minerals, such as pyrites and silicates, in the presence of oxygen and water. It is a significant ore of iron, particularly in certain types of deposits like bog iron ore. It is also used as a pigment in paints and cosmetics, and in some historical contexts, it was used as a source of dye. Due to its widespread occurrence and formation processes, goethite is also important in understanding soil formation and the geochemistry of iron.