﻿Cross and Eakins — Ptilolite. a new Mineral. 119 



ing of pale bluish chalcedony, and upon this is deposited the 

 above mentioned white mineral in most . delicate tufts and 

 spongy masses composed of short hair-like needles, loosely 

 grouped together. These needles when examined under the 

 microscope are found to be colorless, transparent prisms, the 

 average diameter of which is less than 0*001 mm . The termina- 

 tions of unbroken prisms are square, indicating the probable 

 presence of a basal plane, parallel to which there are transverse 

 fissures, as of cleavage. The extinction of the stouter prisms 

 in polarized light is parallel to the prismatic axis, but the mul- 

 titude of smaller ones are so delicate that they do not affect 

 polarized light perceptibly. 



In removing the mineral from the cavities, for chemical 

 analysis, a small amount of chalcedony from the underlying 

 coating, which scales off readily, was unavoidably mixed with 

 the fine hairs. A separation was effected by throwing the un- 

 powderecl material into water and stirring, the spongy aggre- 

 gates resolving readily into a cloud of minute white spicules 

 which remained suspended while the solid particles of chalce- 

 dony with attached needles sank. After standing a few mo- 

 ments the supernatant liquid was poured off, this still contain- 

 ing in suspension the greater portion of the needles, which did 

 not completely settle for several hours. Separation of the 

 needles from other substances was thus made very complete 

 and more than 0*5 gram of pure material secured for analysis. 

 The result, with derived ratio, is as follows (L. Gr. Eakins) : 



Si0 2 _ 70-35 -r- 60= 1-1725 or 10-06 or 10 



A1 9 Q 8 _.ll-90-7-102=0-1166 1*00 1 



CaO 3-87-^- 56 = 0-0691 ) 



K o 2-8'8-t- 94 = 0-0301 V 1116 0-96 1 



Na„0 0-77— 62—0-0124) 



HO 10-184- 18=0-5655 4'86 5 



99-90 



Special care was taken with the water determination of the 

 above analysis. The mineral began to lose water at a very 

 low temperature and even on drying in the air bath at 100° C. 

 there was a noticeable loss; the amount thus lost, however, 

 was found to be regained upon exposure to the air, and before 

 the analysis was made the material was allowed to remain 

 loosely covered for several days. 



The loss of water, beginning at 100° C, continued steadily 

 until at a temperature between 300° and 350° C. all the water 

 was expelled, and continued heating at full redness occasioned 

 no further loss. ISTo line of demarkation could be detected at 

 which the loss temporarily ceased, to begin again at a higher 

 temperature, and thus no ground would seem to exist for con- 



