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BY HERBERT Fox. The following few notes, though possessing no claim to originality, may, perhaps, be of some interest, by directing attention to a group of minerals, some of which are of undoubted economic importance, while others afford examples of some of the large number of chemical compounds existing in nature.
Compounds of Manganese are very widely distributed, though the element itself is never found free in a natural state. Black oxide of manganese, a substance long used to decolourize glass, and called magnesia nigra, from its resemblance to the load-stone, was formerly included among the ores of iron. Towards the end of the eighteenth century, it was proved that the metal contained in this mineral is distinct from iron, and possesses characters peculiar to itself; and, in the year 1774, Gahn extracted from it the metal manganese. This may be obtained by reducing the dioxide with charcoal or soot at a high temperature. A carbide of the metal is then formed corresponding to cast iron, which may be refined by heating it with manganese carbonate. As thus obtained the metal has a greyish white colour, and a fine grained structure ; it is very brittle, and rapidly oxidises on exposure to the air. Its specific gravity is about 8. It is almost infusible, and readily attacked by mineral acids with evolution of hydrogen.
The form in which manganese is used in the arts is that of a naturally occurring oxide, or that of some compound manufactured from one of these, and, as its applications are very numerous, large quantities of these ores are consumed.
The imports into Great Britain for the years 1879-1881, were as follows:
1879............. 12,172 tons, value £45,870.
of which the following quantities were imported into Liverpool :
1879.......... 5,110 tons, value £19,846.
£30,727. London, Glasgow, and some of the towns on the east coastNewcastle, Hartlepool, and Middlesborough, also receive large quantities of manganese.
These ores come principally from the Black Sea, Spain, New Zealand, California, and South America. England itself, in 1881, produced upwards of 2,300 tons; Wales upwards of 300, and Ireland about 250 tons; a total of about 2,900 tons, represented in value by over £6,000. These figures show a large increase as compared with the previous two years, the manganese mined in Great Britain and Ireland, in 1879, being only about 820 tons, valued at about £1,500. The total quantity of manganese ores consumed annually in Great Britain, at present, may be estimated at from 20,000 to 25,000 tons.
These ores consist mainly of pyrolusite, psilomelane, and wad, and are largely used in the manufacture of chlorine, of iron and steel, of glass and pottery, by electrical instrument makers in the manufacture of Leclanche batteries, by oil boilers and varnish makers, and also for bleaching tallow and fat. Considerable quantities are consumed in the manufacture of the sulphate and borate of manganese, which are used as “driers'' in boiling oil, the borate, however, being made principally, if not entirely, on the continent.
Although the uaturally occurring oxides, pyrolusite, psilomelane, wad, &c., are the chief ores of manganese possessing economic value, perhaps it will not be altogether unprofitabie to glance briefly at the properties and occurrence not only of these, but also of some of the rarer of manganese minerals, more particularly with reference to those features by which they may be most readily identified.
As regards the general properties of manganese minerals before the blowpipe, or when treated with chemical reagents, the manganese can be readily detected in substances containing, besides manganese, no other metallic oxides which give coloured beads with borax or microcosmic salt, by simply dissolving them in those fluxes on the platinum wire in the oxidising flame, and then treating the bead with the reducing flame. The hot beads appear amethyst red, but on cooling, are red inclining to violet, and lose their colour when treated for some time in the reducing flame. Microcosmic salt is not so intensely coloured as borax, and loses its colour in the reducing flame much sooner. When a small proportion of other colouring cxides is present they alter the amethyst colour obtained in the oxidising flame slightly, or not at all, but occasionally show their own colour when the manganese colouration has disappeared under the reducing flame.
A method by means of which manganese can be detected in minerals when present only in exceedingly small quantities, is to fuse the substance with two parts of soda and one part of nitre on platinum foil, in the oxidising flame. The oxide of manganese dissolves in the soda to a transparent green mass, consisting of manganate of soda, which flows round the undissolved portion, and is coloured distinctly bluish green when cold.
Minerals containing any oxide of manganese higher than the protoxide evolve chlorine when heated with hydrochloric acid.
If the substance contains or consists of a metallic sulphide or arsenide, it must be heated on charcoal before the above tests for manganese can be applied.
Among the various minerals, differing considerably in chemical composition, of which manganese is an essential constituent, we find the following :
Pyrolusite.—This is one of the most important ores of manganese. It crystallises in forms belonging to the orthorhoinbic system, but is frequently found without any distinct crystalline form. H. 2–2.5. G. 4:82. Lustre, metallic. Colour, iron black, dark steel-grey or sometimes bluish. Streak, black, or bluish black. Opaque and rather brittle. Compo
sition, when pure, Mn 02 Mn 63.2%; 0 36.8% It may be distinguished from psilomelane by its inferior hardness and by its generally being crystalline.
It is found in many places on the Continent, and in America. Hausmannite, - Tetragonal. Cleavage, basal, nearly
. perfect. Also granular-massive. Particles strongly coherent. H. 5.55. G. 4.7. Lustre, submetallic. Colour, brownish black. Streak, chesnut brown. Opaque. Fracture uneven. Composition, Mng 04, Occurs with porphyry, along with other manganese ores, in fine crystals, near Ilmenau,' in Thuringia, Ilefield in the Harz, also reported from Alsace.
Braunite.—Tetragonal, also massive. H 6–6.5. G. 4.75—4.82. Lustre, submetallic Streak and colour, dark brownish black. Fracture, uneven. Brittle. Composition, M112 08. Marceline, an impure variety, contains silica. Occurs both crystallized and massive in veins traversing porphyry at Oehrenstock, near Ilmenau, and at Elgersberg.
Manganite.—Orthorhombic, crystals longitudinally striated and often grouped into bundles, also columnar, seldom granular, stalactitic. H.4. G. 4.2—4'4. Lustre, submetallic. Colour, dark steel grey-iron black. Streak, reddish brown, sometimes nearly black. Opaque ; minute splinters, sometimes brown by transmitted light. Fracture, uneven. Composition, M12 O3 + H2 O, containing, when pure, Mn, O3 =89.8%. H20=10.2.%. Occurs in veins traversing porplıyry, associated witli calcite and barite at Ilefield, in the Harz, Ilmenau and Oehrenstock in Thuringia, in Sweden and Norway, in Nova Scotia, New Brunswick, and other places in North America. In our own country it is found in Cornwall, Cumberland, Devonshire, and Somersetshire; in Aberdeenshire, Scotland, and in several places in Ireland.
Varvacite.-H. 2:5—3. G. 4.283—4.623 may be considered as an altered manganite, consisting largely of pyrolusite.
Psilomelane is found in massive or botryoidal masses. Colour, black or greenish black. Streak, reddish or brownish black. Shining. H. 5–6. G. 4-4.4. Composition, essentially hydrated peroxide of manganese. It also contains some baryta or potash, and is a compound somewhat varying in its constitution. It is an abundant ore, and is associated usually with pyrolasite. Oxide of cobalt has been detected mixed with the ore. It occurs in the same localities as pyrolusite, and the two are often in alternating layers.
Wad is the name given to certain ores of manganese occurring in amorphous and reniform masses, and sometimes incrusting or as stains. They are mixtures of different oxides, and cannot be considered as chemical compounds or distinct mineral species. The principal varieties are Boy Manganese, Jsbolite (a wad containing Coo) and Lampadite or Cupreous Manganese, (a wad containing 4 % to 18 % Cuo, and often Cod.) They are most probably the results of the decomposition of other ores, partly of oxides, and partly of manganese carbonates.
The above enumerated minerals are naturally occurring oxides. When heated in a closed tube they yield more or less water, and some give off oxygen. Heated with HCI they evolve Cl. The small amount of baryta contained in brauuite, lausmanuite, and psilomelane, can often be detected by the feeble, yet distinct baryta flame produced by a small splinter, especially after moistening with H Cl.
Rhodocrosite or Dialloyite is a native carbonate of manganese, part of the manganese being generaliy replaced by lime and often by magnesia or iron. It occurs in rhombohedral
ystals, also more commonly in globular and botryoidal masses of radiated structure. H. 3.5-3.5. G. 3:4-3:7. Lustre vitreous or peariy, usually pink or rose coloured. Streak, white. Translucent to opaque. Before the blowpipe it decrepitates violently. Dissolves in fluxes with effervescence, and reacts like oxide of manganese containing iron. It occurs commonly in veins with ores of silver, lead, and copper, and with other ores of manganese. It is found in Hungary, Transylvania, the Harz, Saxony. It is abundant in the silver mines of Austin, Nevada, and at Placentia Bay, Newfoundland.