Williams — Eudialyte and Eucolite from Arkansas. 457 



merization of the residue. An oxide so formed might con- 

 ceivably be more stable than the oxide with which we previ- 

 ously worked ; at all events, the two are not necessarily 

 identical. As regards the bearing of these data upon our 

 silicate work, we can hardly offer satisfactory conclusions. 

 Still, magnesium saturated by hydroxy 1 is quite differently 

 combined from magnesium which is but half saturated with 

 that radicle, and in the mixed union in a silicate, the polymeri- 

 zation attending dehydration above referred to could hardly 

 occur. "We are inclined to believe, on the whole, that MgOH 

 in a silicate has a lower order of stability towards gaseous HC1 

 than the compound Mg(OH) 2 ; but this point remains to be 

 proved. We hope to continue this investigation among other 

 silicates ; and we feel confident that the data so far obtained 

 have value quite independently of our conclusions. 

 Laboratory IT. S. Geological Survey, Washington, July 7, 1890. 



Akt. LYIII. — Eudialyte and Eucolite, from Magnet Gove, 

 Arkansas ; by J. Fkancis Williams. 



[By permission of the Geological Survey of Arkansas.] 



Eudialyte. — As long ago as 1861 Professor C. U. Shepard* 

 discovered small nodules of a brilliant crimson mineral in the 

 feldspar of the elseolite rock of Magnet Cove, Arkansas. He 

 at first supposed this mineral to be corundum, but after 

 testing its hardness (which he found to be less than 6*), and 

 observing that it gelatinized with hydrochloric acid, he decided 

 that it was eudialyte. From that time the occurrence of this 

 mineral in Arkansas has been mentioned in most text-books of 

 mineralogy f on Professor Shepard's authority, but not until 

 very lately has the subject been revived. During the last 

 year William J. Kimzey of Magnet Cove has found a number 

 of good crystals and also a considerable quantity of the nodular 

 material. Hidden and Mackintosh have published a note in 

 this Journal,^: in which they describe this nodular, rose-red, 

 nearly transparent mineral, and state that it is probably eudia- 

 lyte, and identical with that discovered by Shepard. 



During a recent visit to Magnet Cove, in the interest of the 

 Geological Survey of Arkansas, I was fortunate enough to 



* This Journal, II, xxxvii, 405, 1864. 



f System of Mineralogy, J. D. Dana. 5th edition, p. 249. Lehrbuch der Min- 

 eralogie, G. Tschermak. 2d edition, p. 522. Elemente der Mineralogie, Nau- 

 mann-Zirkel. 12th edition, p. 745, etc. 



\ Am. Jour, of Sci., Ill, vol. xxxviii, 494, 1889. 



Am. Jour. Sci.— Third Series, Vol. XL, No. 240. — Dec, 1890. 

 29 



