LIMONITE or BROWN IRON-ORE, a natural ferric hydrate named from the Gr. XetAc'ev (meadow), in allusion to its oc currence as bog-ore in meadows and marshes. It is never crys tallized, occurring in earthy or compact masses which are some times mammillated, botryoidal, reniform or stalactitic and may have a fibrous internal structure. Its hardness is about 5, and its specific gravity varies from 3.5 to 4. The colour is yellow to brown. Limonite gives a brown streak, which distinguishes it from haematite with a red, and from magnetite with a black, streak. In many cases it has been formed by the alteration of other iron minerals; e.g., by hydration from haematite or magne tite, or by oxidation and hydration from siderite or pyrites. It has been commonly assumed that a series of hydrates of ferric oxide exist in nature, some of which have received specific names —turgite, limonite, xanthosiderite, limnite ; but recent researches by Posnjak and Merwin (Amer. Jour. of Sc., 1919, p. 311), have
shown that there is no foundation for this assumption, there being only one true hydrate, namely, ferric oxide monohydrate, It occurs in two polymorphs as the minerals, goethite (q.v.) and lepidocrocite and in an amorphous condition as limo nite. The latter mineral contains a variable quantity of absorbed and capillary water. The so-called turgite, which has less water than the monohydrate, appears to represent a solid solution of goethite with haematite, together with enclosed and absorbed water. (See also under IRON-ORES.) Limonite abounds at Salis bury and Kent, Conn., in Berkshire county, Mass., and in Ver mont, Pennsylvania, Alabama, Ohio, etc., and is a common ore in many European countries. (F. H. HA.)