NO. 2240. 



NOTES ON MIMETITE, ETC.— WHERRY. 



377 



ing accurate results. This pyramid is taken as the unit 101, and 

 yields the axial ratio for thaumasite : 



<7=0.931± 0.003.^ 



Three other pyramids and the second order prism were also ob- 

 served, making the total number of forms now known on the raintral 

 7. The results of the measurements of the angles of these forms, 

 contrasted with the theoretical values, are given below, and an 

 idealized combination of all the forms in figure 3. The zone of 

 pyramids represents Professor Goldschmidt's harmonic series N3, 

 throe members being absent: 



The combination of forms on the separate crystals are: 



Crystal No. Forms. 



1 c, a, m, e, p 



2 c, m, p, q 



3 c, m, p, q 



4 c, m, p, q 



5 c, a, m, f , p, q 



Majority c, m 



Measured and calculated angles of thaumasite. 



[New forms marked *.] 



THE CHEMICAL CONSTITUTION OF THAUMASITE. 



Thaumasite is one of the few minerals containing three different 

 acid radicals, carbonate (CO3), silicate (SiOs), and sulfate (SO4), 

 as essential constituents; is it to be classed as a carbonate, a silicate, 



1 Axial ratios are often calculated to the fourth, fifth, or sixth decimal place, but when 

 there is a variation of 3 units In the third place such extensions are without signifleanca 



