63 



it was composed essentially of silicate and borate of lime, without any 

 crystalline form. Mr. James A. Dupee supplied me with a larger 

 specimen, and with information respecting its common occurrence in 

 the mines before I had communicated the fact of its composition to 

 this Society. 



Dr. Kneeland recognized the mineral, as a rock called " Tabular 

 spar " at the Portage Lake mines, and Professor Bacon found speci- 

 mens in the collection made by Dr. Kneeland, now in the Society's 

 cabinet, when the subject was before the Society ; thus establishing 

 the identity as well as various localities of the specimens. 



From additional Information received recently, it appears that the 

 rock abounds at several of the mines, and forms part of the gangue 

 rock including copper ; but no formation, or bed of it, has yet been 

 found. 



The Quincy, Marquette, Minnesota, and "Ash-bed" mines contain 

 it, and the Portage Lake and Keweenaw Point rocks include it, in 

 other rocks. 



This mineral is a white compact mass, resembling the coarser kinds 

 of Wedgewood ware. 



Its fracture, approaching conchoidal, leaves sharp edges and splin- 

 ters. Hardness 5.5, or just below feldspar. The masses include 

 trappean silicates in regular crystals, and these often contain oxides 

 of iron and copper. Sp. Gr. 2.911. 



When heated in the closed tube, it gives off water ; at a higher 

 heat a sublimate of boric acid appears. The powder becomes flesh- 

 colored and organic matter is destroyed. 



In the Oxidizing Flame alone, it melts quietly to a transparent 

 globule ; the Reducing Flame expels any bubbles, and the globules 

 are colored by oxides of copper and Iron. Soda in the Oxidizing 

 Flame effervesces and gives a transparent globule, and phosphoric 

 salt develops a silica skeleton. The powder in warm dilute sulphuric 

 or oxalic acid is decomposed, and the addition of alcohol affords a 

 solution, which burns with a green flame. 



Two analyses, embracing the extremes of several, gave : — 



