Limonite

Hardness: 3-4 (Mohs Scale). Color: Yellowish to yellowish-brown. Luster: Pearly to dull. Crystal Structure: Monoclinic, but often found as soft, earthy, and botryoidal masses. Specific Gravity: 2.2-2.5.

Limonite forms as a secondary mineral through the weathering and oxidation of primary iron-bearing minerals like pyrite, magnetite, and hematite in various geological environments, including gossans, bogs, and sedimentary deposits. It doesn't have a specific geological age as it's continuously forming through alteration processes.

Historically, Limonite was an important iron ore, though less so today due to lower iron content compared to other ores. It is still used as a yellow or brown pigment (such as ochre), and occasionally in some lower-grade ceramics.

Limonite is not a true mineral species but rather a mixture of hydrated iron oxide minerals, primarily goethite. It's often found as a weathering product of other iron-rich minerals. Its name comes from the Greek word 'leimon,' meaning 'meadow,' referring to its occurrence in bogs and marshy areas, called 'bog iron.' Limonite has been used as a pigment since prehistoric times, notably in cave paintings.

Limonite can be identified in the field by its characteristic yellowish-brown streaky color, often staining other rocks. It is non-magnetic and often earthy or powdery with a low hardness. It's commonly found in weathered iron deposits, boggy areas, and as a rust-like coating on other rocks. For collectors, it's often of interest when it forms botryoidal or stalactitic habits, or as pseudomorphs after other minerals.