T. L. Walker — Examination of Triclinic Minerals. 185 



drawings as if some of their surfaces were curved. This only 

 means that there are a large number of faces present, so that 

 the figures appear to have curved surfaces, just as prisms of 

 tourmaline often appear to be rounded. There does not seem 

 to be any reason to depart from the opinion of Baumhauer 

 and Becke, who hold that the surfaces of etching figures are 

 never curved but always plane. 



The small number of minerals dealt with in this paper 

 were selected generally because they were most easily obtained 

 in suitable specimens, at other times because they gave defi- 

 nite results. I hope to describe more of the triclinic minerals 

 at- a future time. 



My thanks are due to Babu Nrependra Nath Bose, who has 

 redrawn the figures from sketches made by myself. 



Indian Museum, Calcutta, Nov. 1st, 1897. 



EXPLANATIONS OF PLATE. 



Figure 1. — Corrosion figures such as might be formed on the basal plane of a 



holohedral hexagonal crystal. 

 Figure 2. — Corrosion figures showing the symmetry of the prismatic face of a 



holohedral hexagonal crystal. 

 Figure 3. — Figures on basal plane of muscovite showing monoclinic symmetrj" — 



produced by fused KOH. 

 Figures 4 and 5. — Figures on 0001 and 0001 of tourmaline showing the physical 



difference between the two parallel planes — produced by red hot 



fusion of KHS0 4 and CaF a — tune 2 minutes. 

 Figures 6 and 7.— Figures on 001 and 001 of acid dextro-tartrate of strontium. 



Produced by pressing between very slightly moistened folds of calico 



for 20 seconds. 

 Figures 8 and 9. — Figures on 111 and 111 of axinite— produced by a hot mixture 



of equal volumes of strong _H 2 S0 4 and HF acting for 5 minutes. 

 Figures 10 and 1 1.— Cyanite, 10U and 100— KHS0 4 and CaF 2 at red heat for 1 



to 2 minutes 

 Figures 12 and 13. — Copper vitriol, 110 and 110. Produced by raising the tem- 

 perature of the mother liquor in which the crystals had grown 2°C. 



and allowing the slightly warmed solution to corrode for sixty sec- 

 onds. 

 Figures 14 and 15 — Rhodonite, 001 and 001, hot mixture of equal volumes of 



strong H 2 S0 4 and HF — time 60 seconds. 

 Figure 16. — Albite simply twinned — shows figures on 001 and 001 — same reagent 



as in 14 and 15 — time 30 seconds. 



