nth and Penfidd — LanqfordiU, N^aquehaniU^ etc. 127 



Pseu'to)norp/is of toMqutheniU after tonqfordite. 



Mention has already been made in the first part of this 

 paper and in the original article by Dr. Genth* of fhe occur- 

 rence of lansfordite. On the specimens which were first col- 

 lected no nesqnehonite prisms were visible, but by the time 

 when the second lot was obtained owing to some process B 

 decomposition and recrystallization of the material of the lans- 

 fordite had gone on in the mine, resulting in the formation of 

 the nesquehonite crystals. This recrystallization, resulting in 

 the formation of rather large crystals, had in all cases com- 

 menced at the base of the stalactites and incrustations, leaving 

 the ends of the stalactites still unaltered lansfordite and no real 

 pseudomorphs were found, while the white cryptocrystalline 

 mineral which was formed afterwards from the lansfordite 

 during a period of warm summer temperature has resulted 

 in the production of perfect pseudomorphs, leaving not only 

 the original stalactite form but also the flat crystal faces 

 at the ends well preserved, the stalactites looking like bits 

 of crayon upon the ends of which flat faces had been 

 worn by writing on a black- board. When the specimens 

 were first sent to New Haven in the spring of 1889, there 

 were among them only two specimens, one a small fragment 

 the other a small stalactite, which still showed the parafflne 

 luster, but when the crystallographic work was commenced in 

 the fall of 1889, these two specimens had also lost their luster 

 and become almost completely changed into the opaque white 

 material. The altered stalactites show on a fractured surface 

 with a strong lens a fine fibrous structure, the fibers either 

 radiating or inter-woven like felt and giving a sort of " schim- 

 mer" when held in a strong light. In places it appears dense 

 like chalk or cr3 T pto-crystalline. When carefully crushed and 

 mounted in Canada balsam it shows with the microscope 

 throughout a fine fibrous structure, the larger fibers, which 

 happen to lie on a prismatic or cleavage face giving the same 

 optical properties as nesquehonite. This fibrous material has 

 proved on examination to be like nesquehonite in its chemical 

 composition, an analysis giving : 



Calculated. 

 Ratio. Nesquehonite. Lansfordite. 



COo 28-85 0-656 93 1- 31-88 1 919 



MgO 28-23 706 1*00 V 2899 23-25 



H 2 42-92 2384 337 3' 39-13 5756 



10000 



The analysis and ratio indicate the composition MgC0 3 -SII/), 

 the variation from the theoretical being too little OO, and too 

 much H,0 resulting probably from a slight admixture of 



* Loc. cit. 



