Iron Pyrites (bisulphide of iron) is known as cubic pyrites, yellow pyrites, and mundic. It is generally found in the regular system of crystals, either as a cube or as a pentagonal dodecahedron. (See first system of crystals, ante.) Its colour is yellowish. It is known also as green vitriol when oxidised, and forms beautiful green crystals (copperas). This salt is used in the preparation of Prussian blue and violet dyes. With gallic acid it makes ink.
There are many other “ferruginous” minerals, such as vivianite, green ironstone, white iron pyrites, arsenical pyrites, or mispickel, etc.
A carbonate of iron, called chalybite, or spathic ironstone, is very abundant in nature, and forms obtuse rhombohedrons. It is very useful for the production of steel, as it forms the clay iron ore found in coal districts in combination. In a fibrous form it is known as sphærosiderite. It is a most useful mineral.
Chrome iron (chromite) is useful for the preparation of chromium compounds. It crystallizes in the cubic system. It is magnetic, especially when treated. Chromic acid forms scarlet “needle” crystals, and by its assistance chromate of lead, or chrome yellow, is prepared. (Chromate of lead is found in a native state as crocoisite). See Chromium.
Manganese is contained in several minerals. It usually occurs as an oxide. It colours minerals variously. In a pure state manganese is white and brittle. The chief minerals are—
Pyrolusite (the binoxide of manganese of commerce) occurs in crystals. It is black. It is used in the preparation of chlorine and oxygen. The other minerals are known as manganite, which is also found associated with pyrolusite, as are hausmannite and braunite, the other oxides.
Nickel and Cobalt are generally found together, both being similar, and the minerals are compounds of arsenic or sulphur, and occur under similar circumstances. The principal are of Nickel and of Cobalt—
- Sulphide of nickel (ullmanite).
- Arsenical nickel (nickeline).
- Nickel glance (gersdorffite).
- Nickel pyrites (siegenite).
- Arsenical cobalt (smaltine).
- Cobalt glance (cobaltine).
- Cobalt bloom (erythrine).
- Cobalt pyrites (linnæite).
Nickel ores are used for extraction of the metal, which is used as a substitute for silver. The name is derived from the German, kupfernickel, or false copper. It was discovered in 1751.