MINERAL FROM INVERNESSHIRE. Ill 



per cent. 



Silica 55-02 



Alumina 3*37 



Ferric oxide 19-03 



Ferrous oxide 3*83 



Calcic oxide 2*53 



Magnesic oxide 12*95 



Sodic oxide 1-74 



Phosphoric oxide -33 



Loss on ignition 1-45 



100-25 



These data point to Si^ R R3, or Sig (|S,+|ilJ as the formula for 

 the mineral, and show it to belong to the bisilicate species, the oxygen- 

 ratio for the bases and silica of this species being as 1 : 2, and the 

 general formula E Si^, or Sig (^M, Eg), although, so far as we are 

 aware, it is not identical with any known member of this series. 



The general formula Sig (|R, -i-Eg) would seem to point to its re- 

 lation to segirite, a member of the amphibole group. In colour and 

 general appearance, however, it more resembles crocidolite, a member 

 of the amphibole subgroup, though there is no satisfactory agreement 

 between the analysis of the last-mentioned mineral and that of the 

 subject of this memoir. 



If we suppose that in the formula Sig (JE, ^Eg) 3E3=Mg2+Fe, 

 and that E represents a molecule of the sesquioxide of iron, and 

 keeping in view that the monoxide group, lime, magnesia, soda, and 

 ferrous oxide are mutually replaceable, the above figures point to 

 6 SiO^, FePg, FeO, 2 MgO as the formula of the mineral. 



Properties : — Soft blue amorphous substance, sp. gr. 2-01, unacted 

 upon by acids except when in contact with them for some time. 

 On ignition it changes to a light-brownish powder. Between the 

 poles of a battery it fuses to a metallic bead slightly magnetic. 



In conclusion, we thank Professor Frankland for permitting the 

 analyses to be performed in his laboratory. Professor Judd for valu- 

 able hints received, and Messrs. LinneU and Shilton for assistance in 

 preparing and analyzing some of the specimens. 



Discussion. 



Prof. Maskeltne expressed a hope that purer specimens would 

 be obtained, and praised the authors for the discretion and caution 

 they had exercised in not giving a new name to this substance. 



