72-i DR JOHN MURRAY AND MR ROBERT IRVINE ON THE 



higher oxides of manganese found cither in sedimentary strata or in the ores of 

 veins.* 



The Ores of Manganese. — The ores of manganese and iron are almost the only 

 metalliferous minerals that occur in stratified beds. The manganese ores are as widely 

 distributed as those of iron, but they are only rarely found in any considerable quantity, 

 while those of iron are often present in very extensive beds. The principal manganese 

 ores are oxides, and so intimate is their connection with those of iron that manganese occurs 

 as a constituent in all iron ores ; manganese dioxide was at one time, indeed, regarded as an 

 iron ore. The ores of iron and manganese have evidently had a similar origin. In the 

 United States, nodules of manganese dioxide form the bulk of the manganese ores, and 

 they either are or were embedded in calciferous shales. They occur in pockets or sheets, 

 the individual nodules varying from the size of a pin's head to masses weighing tons. In 

 Russia, Chili, and other countries the manganese ores appear, from the descriptions, to be 

 similar to those of the United States, and to have been laid down under similar physical 

 conditions. The manganese and iron ores occur in the stratified rocks of all geological 

 formations, and they appear to have had their origin in the disintegration of the 

 crystalline rock-masses of the region in which they are found. The manganiferous 

 minerals and ores of veins and lodes have, in all probability, had a similar origin in the 

 alteration of the crystalline rocks of the vein- walls and deposition from aqueous solution.t 



as in (1). The deficit (i.e., the difference hetween the above two determinations) due to exhaustion with dilute acetic 

 acid we assume to be present as carbonate of manganese. 



In many of the rocks and minerals examined in this manner we found the manganese wholly combined with carbonic 

 acid, in others partly with carbonic acid and partly with silicic acid ; in some cases it is present as peroxide ; it may 

 exist in all three forms in the same rock, whilst in the majority of minerals it exists combined with silicic acid alone. 



The felstones of the upper area of the Clyde basin seem to contain all their manganese in a soluble condition, pre- 

 sumably as carbonate. These rocks effervesce on treatment with dilute acids. If the deposits of the Clyde Sea- Area 

 contain more peroxide than the deposits of other similar areas, this may be due to the soluble condition of the manganese 

 in these felstones. In the laboratory, when a portion of these rocks was simply fused or fritted without fluxing 

 material, the carbonic acid was expelled, and the bases were found in the cooled mass to be combined with silicic acid 

 alone, as a silicate or silicates insoluble even in strong hot hydrochloric acid. Even when ten per cent, of carbonate 

 of lime was added to the pulverised felstone, and the mixture fused, the silicates in the fritted material were insoluble, 

 showing the acid nature of this class of rocks. This exjieriment shows that in the presence of silicic acid (or acid 

 silicates) carbonates are decomposed by heating, silicic acid taking the place of the carbonic acid expelled, and also that 

 the manganese found in these rocks has really been infiltrated as carbonate into even the heart of the felstone. These 

 felstones are hard compact rocks, and contain no water which can be expelled even at 400° F. (204° - 4 C), nor do they 

 absorb water, even when soaked in it for twenty-four hours. 



We are indebted to John Young, Esq. LL.D., Hunterian Museum, Glasgow; Mr C. Maclaren Irvine, Lanarkshire; 

 .1. S. Dixson, Esq., Hamilton ; Mr Durham, Newport, Fife ; Mr Pearcey, and Captain Turbyne, for specimens of 

 rocks, drainage waters, and deposits from the Clyde area. 



* Professor Clarke estimates that manganese makes up about O08 per cent, of the earth's crust. (Bull. Phil. 

 Soc. Washington, vol. xi. p. 138, 1892). 



+ The following are the principal manganese minerals : — Pyrolusite, (Mn0 2 ) ; hausmannite, (Mn.,0 4 ) ; braunite, 

 (Mu.Pg) ; manganite, (Mn 2 3 ,H 2 0) ; psilomelane, (Mn0 2 , united with some protoxide, as of Mn.Ba.K., or H,) ; dialogite 

 (MnCOg). 



The following are oxides — Jacobsite, crednerite, chalcophanite, fianklinite, pyrochroite. 



Sulphide (blende)— Alabandine (MnS). 



Anhydrous Carbonates — Breunnerite, siderite, mangano-calcite. 



Hydrated Sulphates— Lankite, mellardite. 



Eydrated Phosphates (the numbers are percentages of MnO in the mineral) — Fillowite (40), heterozite, dicksonite 

 (2'>), fairfieldite (16), neddingite (46), eosphorite (24), childrenite (9), tuplite. 



