376 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 54. 



thaumasite at Longbanshyttan.* A supplementary note calling atten- 

 tion to this was then published in the American Mineralogist. ^ 



The crystals described by Doctor Flink are remarkably like those 

 from West Paterson; they agree in size, habit, frequency of double 

 termination by base, rarity of pyramid faces, dullness of base, etchings 

 on prism faces, etc. He found two crystals with measurable pyramid 

 faces, on one of which two angles, from pyramid to prism, proved to 

 be 42° 24' and 42° 26'; the corresponding angle with the base (p) 

 is 47° 35', whence the axial ratio c=0.9479. No other forms were 

 observed. 



Some uncertainty would naturally be attached to a ratio based 

 on two measurements on a single crystal which was admittedly rather 

 poorly developed. When compared with the results obtained by the 

 writer on the New Jersey crystals, which are given in full below, it 

 will be seen that the difference between the two sets of measurements 

 is but 30', and the corresponding difference in axial ratio 0.017 ; but 

 since the writer's value is based on 26 measurements, on four forms, 

 on five different crystals, it is believed to be nearer the true axial 

 ratio for the species. 



The crystals measured are from 0.5 to 1.5 mm. long and 0.3 to 0.7 

 mm. in diameter. The basal planes are dull, and yield only faint 

 reflections; the pyramid faces are none too brilliant, and are mostly 

 somewhat curved, so that they distort the image of the signal a little ; 

 the prism faces are the best of all, yielding brilliant images, although 

 the existence of intergrowth with subparallel crystals makes itself 

 evident in frequent multiplicity of images. None of the termina- 

 tions is perfect, only from one to four of the possible six pyramid 

 faces being developed; nor were any of the crystals found to be 

 doubly terminated with pyramids ; in every case the opposite end to 

 that showing pyramid faces is terminated by the base alone. This 

 suggests that the mineral is hemimorphic, but this could not be con- 

 firmed by etch-figures, since etching with dilute acids and with water 

 containing carbon dioxid yielded nothing but narrow grooves with- 

 out definite crystallographic features. The rather poor quality of 

 the faces renders the measurements somewhat unsatisfactory, but 

 the axial ratio of the mineral can certainly be regarded as estab- 

 lished and the presence of several new forms proved. 



One pyramid appears on all five crystals, yielding fairly good reflec- 

 tions in several instances, and its p was found to average 47° 5'±:15'. 

 This is evidently the same form observed by Doctor Schaller, the 

 discrepancy in angles being due to the fact that he was unable to 

 obtain definite signals with his crystal, and so was obliged to locate 

 the pyramid by maximum illumination, a method incapable of yield- 



1 Geol. For. Forh., vol. 39, 1917, pp. 447-452. 

 'Vol. 2, 1917, p. 125. 



