MorAlinKM'.M IN NATAL. I55 



Sulphur 4-4% 



Iron 2.9% 



Molvbdenum i . i% 



Alkalies Nil. 



Unfortunatelw lack of the necessary apparatus i)reventecl tlie 

 determination of the projiortion of carbon, ])ut its value is 

 obviously less than 6^f . 



The sulphides are conseciuently present in the f<illn\vin<( ])n)- 

 portions : — 



Pyritc or Mar casite 6.53% 



Molybdenite i.-'^S'/r 



Most interesting are the oxidation products of the sulphide 

 minerals in the rock. Some surfaces and joint planes are coated 

 with a thin incrustation of bright yellow Molybdic Ochre, a 

 mineral which is not trioxide of molybdenum, as usuallv stated 

 in text-books, but, as pointed out by Schaller,* a hydrous ferric 

 molybdate !'>/).. .3MoO;<.7iH./), formed by the oxidation of 

 molybdenite in the presence of pyrite or marcasite. 



Its identification was confirmed by chemical and o])tical tests. 



In one case a bright lemon ^-eHow efflorescence formed on 

 the specimen in the cabinet after collection in the form of small 

 pin-points of a soft substance, which proved to be not molybdic 

 ochre, l)Ut granular sulphur in j^art, originatmg most ])robably 

 from the alteration of the molybdenite. On the same sample very 

 small cr}'Stals of green ferrous sul])hate had develo])ed from the 

 iron sulphide. 



On the exposed face of sandstone there was a large i)atch of 

 a thin incrustation which ranged in colour from nearly black to 

 an intense prussian blue ; the substance is soluble in water, and 

 gives a strong reaction for molybdenum, and must, therefore, be 

 the rare mineral Ilseuiannite, AIoO„.4J\Io03, so far only known 

 from Bleiberg, in Carinthia,t as a product of decomposition of 

 wulfenite, molybdate of lead, and from Cripple Creek,| Colorado, 

 as an alteration of molybdenite. In Natal, therefore, the mode 

 of origin of this uncommon mineral is identical with that in 

 Colorado. 



The walls of the adit are coated with a friable yellowish in- 

 crustation which proved to be principally Aluminite, a basic 

 aluminium sulphate with a certain amount of iron, but devoid of 

 lime, magnesia or potash. A similar substance was found below 

 the undercut base of the sandstone outcrop, where it was pro- 

 tected from the rain and is harder and more stalactitic in charac- 

 ter, and dull whitish in colour, with tints inclining from yellow- 

 brown on the one hand to ])ale blue on the other; it is of interest 



* W. T. Schaller, .Imer Jour Sci.. 4II1 series, 23 (1907), 297. 

 t W. Lindgren and F. L. Ransonie, U.S. Geol. Surv., Prof. Paper 54 

 (1906), 124. 



I E. S. Dana: "A System of Mineralogy," p. 202. 



