134 On an Artificial Diopside Rock. 



presenting faces ; and on placing one of these on the gonio- 

 meter the nature of the mineral was placed beyond doubt. 



It is, in short, diopside, with the forms m, {110}; Z>, {010}; 

 o, {2 2 1} ; s, {1 1 1}, as is seen from the following comparison 

 of the calculated with the measured angles : — 



Calculation. Found. 



\mm' = 87 5 

 \mb = 43 32J 

 lab =46 27i 



87 



18 45 



43 



36 



46 



21 



35 



391 



59 



38 



\jn f s = 58 46 



ms = 78 56 78 44 



Two specimens of this artificial rock were analyzed by Mr. 

 Gilchrist, and gave the numbers in columns 1 and 2 : — 



FeO 

 Al 2 O s 

 CaO 

 MgO 



Si< 



(1) (2) (3) (4) 



1-63 1-63 1-38 



2-47 2-47 



19-50 21-00 25-05 25-93 



14-45 16-49 17-36 18*52 



63-00 58-75 56-03 55-55 



101-05 100-34 99-82 100-00 



These analyses correspond very nearly to that of a diopside 

 containing one equivalent each of calcium and magnesium ; 

 but with an admixture of silica in the one case of about 17, 

 and in the latter case of 14*5 per cent, in excess. 



This ingredient is doubtless a mechanical adjunct to the 

 diopside, and is derived from the silica brick, to the presence 

 of which the formation of the diopside is due. The portions 

 of the mass in which the alkaline earths are in excess do not 

 contain the diopside, and they gradually become slaked on 

 exposure to the air. The composition of such an ideal diop- 

 side would be that indicated by the numbers in column (4), its 

 formula being (Ca J MgJ) SiO s . 



Column (3) represents the results of an analysis by Rammels- 

 berg of a diopside from Retzbanya, which is given for compa- 

 rison with that of the artificial diopside rock. The artificial 

 production of an augitic mineral is no new fact ; but the for- 

 mation on a considerable scale of a veritable diopside rock 

 appears to be as novel as it is interesting. 



