M. Berth ier's Description of' Nontronite. ^ 161 



it is to this circumstance that we owe the discovery of a new 

 mineral, which I shall describe under the name of Nontronite. 



The stratum of the manganese of Dordogne is superficial. 

 It consists of ferruginous clay, mixed with quartz, sand, and 

 a little mica. It is^evidently of the same formation as the stra- 

 ta of iron called alluvial, which exist in the country. 



The ore of manganese is found in irregular masses more or 

 less considerable in the ferruginous clay ; it is a mixture of 

 the hydrate of the deutoxide of manganese, of the peroxide, 

 and of the barytic combination which prevails in the ore of 

 Romaneche. 



Nontronite was discovered by M. Lanoue in the ore of 

 manganese wrought near the village of Saint Pardoux. It is 

 disseminated in amorphous onion-shaped masses, commonly very 

 small, and seldom so large as the fist. Hence round masses 

 are almost never pure, and divide easily into smaller masses 

 quite irregular, all these small masses being coated with a slight 

 black pellicle, which is oxide of manganese, and they are often 

 mixed with micaceous clay of a dirty yellow colour, so that 

 when we cut the mineral, and polish it, it presents the appear- 

 ance of a variolite. It is nevertheless easy to procure Nontro- 

 nite pure by a careful selection of it. 



This mineral is compact, of a pale strati' colour, with a fine 

 canary yellow slightly greenish. It is opaque, unctuous to 

 the touch, and very tender. Its consistence is the same as 

 that of clay ; it is easily scratched with the nail ; it takes a fine 

 piolish and resinous lustre under the friction of softer bodies; 

 it is flattened, and grows lumpy under the pestle, instead of 

 being reduced to powder; it exhales an odour when breathed 

 tfpon, and does not act on the magnetic needle. When im- 

 mersed in water, it disengages many air-bubbles ; it becoflies 

 translucent at the edges with losing its form, and if at the end 

 of some hours it is taken oUi of the water, atrd weighed after 

 it is wiped, it is found to have increased onef-tenth in its 

 weight. When heated in a glass tube, it loses its water with 

 a slight heat, and takes the colour of a dirty re'd OxMe Of iron. 

 When calcined in a crucible, it assumes the satne aspect, and 

 its weight is diminished from 0.19 to 0.21. After calcination"^ 

 it is sensibly magnetic. 



