Knopf and Schaller — Tioo New Boron Minerals. 323 



Akt. XXXVI. — Two New Boron Minerals of Contact-Meta- 

 morphic Origin ; by A. Knopf and W. T. Schaller. 



The material upon which the following paper is based was 

 gathered by one of the writers (Knopf) during^the summer of 

 1907 while engaged in an investigation of the Alaskan tin 

 deposits for the TJ. S. Geological Survey. The chemical and 

 crystallographical work was performed in the laboratory of 

 the Survey by Waldemar T. Schaller. 



The Alaskan tin deposits of known economic importance are 

 limited to the extreme western part of the Seward Peninsula, 

 about 100 miles northwest of the city of Nome. They are 

 genetically associated with granitic intrusives which have 

 invaded limestones of Paleozoic age. Along the margins of 

 the granitic bosses an intense pneumatolytic contact-meta- 

 morphism has frequently been produced and a considerable 

 variety of minerals developed. The largest granite boss of the 

 region is that of Brooks Mountain, and the most energetic 

 contact action is displayed along its periphery. The granite 

 has a coarse porphyritic habit, and consists of phenocrys'ts of 

 orthoclase an inch in diameter, and of smoky quartz, half an 

 inch in size, embedded in a coarse to fine-grained granular 

 matrix of feldspar, quartz and biotite. Along the margin of 

 this intrusive body, the granite is often strongly tourmalinized. 

 No tin deposits are known to be associated with this particular 

 granite, but a few miles to the south of it they occur in con- 

 nection with a smaller intrusive. 



On the northwest flank of Brooks Mountain a prospect cut 

 has been opened on a showing of contact metamorphic min- 

 erals occurring in marmorized limestone 10 feet from the 

 granite contact. Examination of this deposit showed that an 

 unknown mineral, which subsequent investigation has shown 

 to be a new boron mineral, was present in considerable abund- 

 ance. We propose for it the name hulsite, in honor of Mr. 

 Alfred Hulse Brooks, geologist in charge of the Division of 

 Alaskan Mineral Resources. In the hand specimen brown- 

 green vesuvianite, magnetite, hulsite and rarely brown garnet 

 occur scattered through a matrix of coarse white calc-spar. 

 Occasionally some fiuorite is visible. The characteristic forms 

 of vesuvianite are a {100}, m {110},/ {120}, c {001}, _p fill}, 

 if {331}. Less prominent, h {130], 8 {113}, t {112}, I {221} 

 and others. Treated with fiuorite mixture, it gives a distinct 

 boron flame, and is therefore regarded as probably belonging to 



