220 Dr Brewster's Description of' Withamite, 



This mineral is not acted upon by acids either cold or hot ; 

 and it does not phosphoresce on a heated iron. The following 

 experiments upon it with the blow-pipe were made by Mr 

 Haidinger. 



When placed alone upon charcoal it intumesces, and as- 

 sumes a shape like cauliflower, but it fuses with difficul- 

 ty, and has the appearance of a dark greenish grey ena- 

 mel. With borax it effervesces, and forms a transparent 

 globule, of a deep yellow colour, when hot, but becoming 

 pale on cooling. The tint in the oxidating flame is slight- 

 ly yellowish, and in the reducing flame greenish. It is dis- 

 solved with effervescence by salt of phosphorus, with the ex- 

 ception of a skeleton of silica. The globule is yellow while 

 hot, but becomes white and opaque, or, at least, opaline, on 

 cooling. With a little soda it fuses with difficulty into a deep 

 green gla£s, but a larger quantity renders it infusible. With 

 soda upon platina foil it gives a green colour, which is purer 

 than that from the epidote of Arendal, but less inclining to 

 blue than that from the pure oxide of manganese, or from the 

 manganesian epidote of St Marcel. Withamite exhibits the 

 same phenomena before the blow-pipe, as the epidote from 

 Arendal, only it is a little more difficult of fusion. Silica, iron, 

 and manganese, are unequivocally indicated among its consti- 

 tuents. Lime is probably one of its ingredients, on account 

 of the intumescence, and the opacity of the globule when 

 melted with salt of phosphorus. 



From these experiments, and from the similarity in the 

 crystallographic form, and composition of the two sub- 

 stances, Mr Haidinger, whose knowledge of minerals is un- 

 rivalled, was disposed to consider Withamite as a new and 

 remarkable variety of epidote. I was therefore induced to 

 re-examine a fine crystal of epidote from Chamouni, which 

 Mr Haidinger gave me for this purpose, and to compare it, 

 as far as I was able, with the Withamite. The result of this 

 comparison, though favourable to the opinion, that these two 

 minerals are closely allied jn their natural history properties, 

 was such as to convince me, that the Withamite exceeds epi- 

 dote both in lustre and double refraction, and very greatly in 

 its ordinary refractive power. This result I was enabled to 

 confirm by another mode of observation. — Mr Somcrvillc had 



