Loadstone, or MAGNETIC IRON ORE, a mineral consisting of a mixture of the ferric and ferrous oxides, or , remarkable for its highly magnetic quality. The name loadstone or lodestone ('leading-stone') is derived from its power of drawing or leading bits of iron; the earliest magnets were pieces of loadstone, and the value of the ore for making a mariner's compass (see COMPASS) was early known: 'the lodestare [polestar] draweth the lodestone as the lodestone the steel.' Loadstone is black, and has a metallic lustre; its hardness = 5.5 to 6.5, and its specific gravity = 4.9 to 5.2. It is one of the most common constituents of eruptive rocks, occurring in these generally in the form of small octahedra or irregular grains. Some rocks, such as certain basalts, contain so much magnetite as strongly to affect the compass. Larger and well-defined crystals are met with in the crystalline schists, more especially in chlorite-schist. Magnetite also occurs massive, associated with other iron ores, forming in some places irregular bedded sheets amongst the crystalline schists, and in other places entering largely into the composition of mountains, as in Sweden—one of the richest iron-bearing regions in the world. The iron-sands which occur here and there in river-beds and along certain sea-coasts consist of magnetite which has been derived from the degradation of eruptive rocks.
Many strange beliefs have been held about the properties of the loadstone, and an interesting account of the true and untrue among these is given by Sir Thomas Browne in his Vulgar Errors (book ii. chaps. 2, 3). Thus, one species was said to attract flesh; again, its operation was hindered by garlic, by the diamond, by quicksilver. Heavy bodies such as chariots of iron could be suspended in the air by systems of magnets arranged. Again, it possessed valuable medicinal properties in cases of dropsy, ruptures, and gout; and had, moreover, magical efficacy to detect incontinence and theft, to divine, and to afford means of communication with absent friends.