162 Williams — Eudialyte and Eucolite from Arkansas. 



crystals were found which were made up of both pink and 

 yellowish brown material, and in these cases it was always 

 found that the former was positive and the latter negative. 



Wilhelm Ramsay * in his " Geologische Beobachtungen auf 

 den Halbinsel Kola " has observed that, in the eudialyte of the 

 nepheline syenite, which he describes, both positive and nega- 

 tive as well as isotropic zones appear, but that no difference in 

 color nor in the indices of refraction between the various parts 

 was detectable. Ramsay's observations were made by means 

 of a selenite plate on sections, which were slightly inclined to 

 the principal axis, while those on the Arkansas mineral were 

 made by means of a quarter-undulation mica plate on sections 

 parallel to the base. 



From the low specific gravity and hardness, as well as the 

 want of complete transparency in the eucolite crystals, it may 

 well be suspected that these crystals are decomposed or weath- 

 ered eudialyte. To these facts may be added the observations 

 that, in cases where eudialyte has begun to weather, it is found 

 in the form of pink grains surrounded by a soft yellowish 

 brown powder, which resembles very closely the eucolite just 

 described. Moreover it is probable that the yellowish coatings 

 observed on the surface of the eudialyte crystals already 

 described are made up of this same brownish yellow mineral. 

 A determination of the amount of water in a specimen of the 

 eucolite would be of use in deciding the question of its origin. 



Both eudialyte and eucolite occur in two places in Magnet 

 Cove ; one, one hundred meters northeast of the point where 

 the Hot Springs turnpike crosses Cove Creek, and the other 

 on " the branch " about 150 meters east of where it empties 

 into Cove Creek. Indications of eudialyte have been observed 

 in the elseolite syenite of Saline County, Ark., on the property 

 of Sol. Nethercutt, about seven miles (11 km.) JST.E. of Benton. 

 (N.W. of S.B. of Sec. 16, 2S. 11 W.) At this point the min- 

 eral was so badly weathered that an exact determination was 

 impossible. 



Besides the segyrite, elseolite and orthoclase of the rock in 

 which the eudialyte occurs, there are found as accessory min- 

 erals beautiful little idiomorphic titanites and apatites. As 

 decomposition products there appear ozarkite (thomsonite) 

 and manganopectolite,f which may be due in part at least to 

 the weathering of eudialyte as well as of the other constituents 

 of the rock. 



Petrographical Laboratory, Clark University, 

 Worcester, Mass., June, 1890. 



* Wilhelm Ramsay. Fennia, Bulletin de la Societe de geographie de Finland, 

 iii, No. 7, pages 42 and 43. 



f J. F. Williams. Manganopektolit. Ein Neues Mineral aus Magnet Cove, Ark. 

 Zeitsch. Kryst. Min., xviii, 1890." 



