Bog Iron-ore

Bog Iron-ore, a mineral of very variable composition, but regarded as consisting essentially of peroxide of iron and water; the peroxide of iron often amounts to about 60 per cent., the water to about 20. Phosphoric acid is usually present in quantities varying from 2 to 11 per cent. Silicic acid, alumina, oxide of manganese, and other substances, which seem accidentally present, make up the rest. Bog iron-ore occurs chiefly in alluvial soils, in bogs, meadows, lakes, &c. It is of a brown, yellowish-brown, or blackish-brown colour. Some of its varieties are earthy and friable, formed of dull dusty particles; some are in masses of an earthy fracture, often vesicular; and some more compact, with conchoidal fracture. It is abundant in some of the northern and western islands of Scotland, and in the northern countries of Europe generally; also in North America. When smelted it yields good iron (see IRON, ORES OF). Bog iron-ore owes its origin to the chemical action of organic acids arising from the decomposition of plants. These acids attack and dissolve the salts of iron which they meet with in the rocks and soils. The solutions thus formed, when they are exposed to the air, become oxidised, and iron is thus precipitated in the form of hydrous ferric oxide, which, along with the various impurities mentioned above, forms bog iron-ore. This mineral occurs frequently in boggy or badly-drained land, forming the hard ferruginous crust known in Scotland as 'moorland-pan.' Considerable accumulations of bog iron-ore or lake-ore occur in the bottoms of lakes in Sweden and Norway, forming with comparative rapidity on the shallower slopes where reeds grow more or less abundantly. According to Ehrenberg, the bog iron-ore in the marshes about Berlin owes its origin largely to diatoms, which separate iron from the water and deposit it as hydrous ferric oxide within their siliceous frustules.