l, a considerable body of rubbish from ancient workings, towards the summit of the metalliferous hill d, l.
m, m, part of this hill covered with rubbish, the result of old workings.
n, the site called Vigneria.
o, houses upon the shore called Marine de Rio, where the workpeople live, and the mineral is kept in store.
p, wooden pier (mole) whence the ore is shipped; terminated by a small tower q.
Compact fer oligiste occurs also in the Vosges, in Corsica, at Altenberg and Freyburg in Saxony, Presnitz in Bohemia, Norberg and Bisberg in Sweden, &c.
The varieties called specular fer oligiste, and scaly fer oligiste, or iron-glance, do not differ essentially from the compact. None of them affects the magnetic needle, and their powder is a red of greater or less vivacity.
8. Red oxide of iron.—The varieties included under this species afford a red powder, do not affect the magnetic needle, and are destitute of metallic lustre. At the blowpipe they all become black, or deep brown; and then they act on the needle. The crystallized variety consists of 70 iron and 30 oxygen in 100 parts. The concretionary kind, or hematite, has a brown-red colour; is solid, compact, and sometimes very hard; its surface may be filed and polished so as to acquire a lustre almost metallic; its internal structure is fibrous, and it exhibits sometimes a resemblance to splinters of wood. Its outer surface is constantly concretionary, mammelated, and presents occasionally sections of a sphere, or cylinders attached to each other. This is the blood-stone of the burnisher of metals. It is a very common mineral. The ochry variety or red-iron-ochre is distinguished from the solid hematite by the brightness of its colour. It is used as a pigment.
9. Brown oxide of iron, brown iron-stone.—This affords always a yellow powder, without any shade of red, which passes sometimes into the bistre brown, or velvet black. At the blowpipe this oxide becomes brown, and very attractable by the magnet; but after calcination and cooling, the ore yields a red powder, which stains paper nearly as red as hematite does; and which is much employed in polishing metals. All the yellow or brown oxides contain a large proportion of water, in chemical combination; and hence this species has been called hydrate of iron. There are several varieties which assume globular, reniform, stalactitic, and fruticose shapes. As impure varieties of the species we must consider some of the clay-iron-ores, such as the granular, the common, the pisiform, and the reniform clay-iron-ore. According to D’Aubuisson, the present species consists of peroxide of iron, from 82 to 84 per cent.; water, 14 to 11; oxide of manganese, 2; silica, 1 to 2. It is therefore a hydrated peroxide of iron; and ought by theory, to consist, in its absolute state, of 81·63 peroxide, and 18·37 water. It occurs both in beds and veins. The œtites or eagle-stones form a particular variety of this ore. On breaking the balls so named, they are observed to be composed of concentric coats, the outside ones being very hard, but the interior becoming progressively softer towards the centre, which is usually earthy and of a bright yellow colour; sometimes however the centre is quite empty, or contains only a few drops of water. Œtites occur in abundance, often even in continuous beds in secondary mountains, and in certain argillaceous strata. These stones are still considered by the French shepherds as amulets or talismans, and may be found in the small bags which they suspend to the necks of their favourite rams; and they are in such general use that a large quantity is annually imported into France from the frontiers of Germany, for this superstitious purpose. When smelted, they yield a good iron.
The variety called granular brown oxide, or bone ore, is merely a modification of the preceding. It occurs in grains nearly round, varying in size from a millet seed to a pea, each being composed of concentric coats, hard outside and soft within. They are generally agglutinated by a calcareous or argillaceous paste; but are occasionally quite loose. This ore occurs in calcareous formations, and is sometimes accompanied with shells, such as terebratulæ. The brittle quality of the iron afforded by it, has been ascribed to the phosphorus derived from the large quantity of organic bodies, with which the ore is frequently mixed. The bog-iron-ore, and swamp iron ore belong to this species.