Am. Jour. ScL.Vol. XXVII, 1909. 



Plate I. 



Photomicrographs. 



a Artificial diopside. Etch pits on 110 produced by action of hot com- 

 mercial HF for 40 seconds. Magnification 200 diameters. 



b Artificial diopside. Etch pits on HO. Exposed to hot commercial HF 

 40 seconds. Magnification 230 diameters. 



c Etch pits on HO of crystal MgSi0 3 50 per cent, CaSi0 3 50 per cent. 

 Time of exposure 40 seconds in hot commercial HF. Magnification 220 

 diameters. 



d Etch pits on HO of crystal MgSi0 3 55 per cent, CaSi0 3 45 percent. Time 

 of exposure in hot commercial HF, 40 seconds. Magnification 440 diameters. 



e Etch pits on 110 Mg-pyroxene (<3-MgSi0 3 ). Exposed 50 seconds in hot 

 commercial HF. Magnification 1065 diameters. 



/ Etch pits on 110 of crystal MgSi0 3 75 per cent, CaSi0 3 25 per cent. 

 Exposed 40 seconds in hot commercial HF. Magnification 230 diameters. 



