siderite (chalybite, spathose iron) Mineral, FeCO₃; sp. gr. 3.8–4.0; hardness 3.5–4.5; trigonal; grey to grey-brown or yellowish-brown, translucent when pure; white streak; vitreous lustre; uneven fracture; crystals rhombohedral with curved faces, but also occurs massive, granular, fibrous, compact, botryoidal, and earthy in habit; cleavage perfect rhombohedral {1011}; widespread in sedimentary rocks, especially clays and shales where it is concretionary and makes clay into ironstone, also as a gangue mineral in hydrothermal veins together with other metallic ores (e.g. pyrite, chalcopyrite, and galena) and as a replacement mineral in limestone; dissolves slowly in cold, dilute hydrochloric acid, which effervesces when warmed.

sid·er·ite / ˈsidəˌrīt/ • n. 1. a brown mineral consisting of ferrous carbonate, occurring as the main component of some kinds of ironstone or as rhombohedral crystals in mineral veins.2. a meteorite consisting mainly of nickel and iron.DERIVATIVES: sid·er·it·ic / ˌsidəˈritik/ adj.

siderite †loadstone XVI; various min. uses from XVIII. In early use — F. sidérite or L. sidērītēs, -ītis — Gr. sidēítēs, — îtis, f. sídēros iron; in later use f. Gr. sídēros; see -ITE.

Siderite

An old name for a loadstone or magnet. The term has also been variously used to indicate a steel-colored stone (possibly sapphire), a blue-colored quartz, carbonate of iron, and meteorites containing iron.