234 Emerson — Corundum and a Graphitic Essonite. 



Aet. XXYIII. — N'ote on Corundur^i and a Graphitic Essonite 

 from, Barkhanisted, Connecticut / by B. K. Emerson. 



Some years ago I received from Mr. W. E. Manchester of 

 Pleasant Yalley in Barkhamsted who is well acquainted with 

 the mineraloo^y of the region, a large block of a heavy bluish 

 black rock which proves to be corundum, and several speci- 

 mens of a very peculiar large garnet which are penetrated by 

 quite thick sheets of graphite. 



The accompanying rock, which seems to be the country rock 

 and which occupies a large area, is a coarse mica schist, which 

 in a northwest direction for two miles abounds in smaller 

 garnets 2-5"^™ across, of red color, accompanied by dark red- 

 dish brown staurolite crystals an inch across, and also cyanite in 

 blackish crisscrossed blades an inch wide and two inches long. 

 ]^ear where the cyanite occurs there comes in above it a fibro- 

 litic gneiss which 1 have, farther north, associated with the 

 Algonkian. This latter rock contains layers, an inch thick ; of a 

 compact or finely fibrous fibrolite (faserkiesel) containing many 

 large grains of magnetite. The mineral proves under the 

 microscope to be made up of almost pure matted fibrolite 

 needles. 



Garnet. — The remarkable garnets occur in well-formed dode- 

 cahedrons above two inches in diameter and extend over a broad 

 area forming a very coarse continuous drusy surface, some crys- 

 tals rising so as to show almost all their faces, others fused into 

 large groups which rise several inches above the surface of attach- 

 ment. They do not, however, present the aspect of crystals which 

 have grown freely into a cavity, since the faces are not pol- 

 ished and continuous but rather dull and often deeply exca- 

 vated with deep and irregular cavities from which some mineral 

 has been removed by solution. In the least weathered crystals 

 there are still large grains of included calcite visible, and we 

 may assume that the mineral which has been removed from 

 the depressions was calcite, that the whole broad surface of 

 great crystals has grown from a base of mica schist up into a 

 bed of crystalline limestone, which has been removed by solu- 

 tion from the surface of the crystals. 



The character of the crystals agrees with this derivation. 

 They are pale honey-yellow to almost colorless, agreeing in 

 tint and general appearance closely with the crystals from 

 Gatineau, Canada, except that they are simple dodecahedrons, 

 are much larger and lack the polished faces, though this may be 

 due to a subsequent weathering. They are doubtless a quite 



