Siliceous Sinier of the Azores. .391 



55. Siliceous Sinier of the Azores. 



Mr. Silliman, 



In examining some varieties of siliceous sinter from the 

 Azores, I have met with one which differs from any hither- 

 to found in Iceland or other countries, where the substance 

 occurs under those forms usually seen in our cabinets. 

 From the island where this variety occurs (St. Michaels) it 

 might perhaps be distinguished by the term Michaelite. 

 From the specimens before me I send you the following 

 description. Your's, &c. 



J. W. WEBSTER. 



External Characters. 



Color snow white, reddish and yellowish white, passing 

 in some specimens to yellowish grey. 



It occurs in long slender (capillary) filaments, from one 

 to four inches in length. 



The filaments cross each other in every direction. 



On the cross fracture, viewed with a microscope, a lus- 

 tre between vitreous and pearly is observed. 



It is translucent. Brittle and light. 



When reduced to powder and rubbed on glass it scratch 

 es it. 



Specific gravity 1.866. 



Chemical Characters. 

 infusible without addition before Brooke's blowpipe 



Constituent Parts. 



100 



Six grains in fine powder, intensely ignited in a piatina 

 crucible for fifteen minutes, lost 0.98125 grains, equal to 

 16.35 per cent. ; it is an hydrate of silex and is composed of 



Silex, - 83.65 



Water. - - 16.35 



