1,SS2.] OJI [Geuth. 



6. Corundum, altered into Cyaniie. 



a. In the gravel, two miles West of Statesville, Iredell Co., N. C, an 

 interesting specimen has been found, consisting of a nucleus of pink 

 colored corundum, around which is crystallized pale blue cyanite which 

 latter has evidently resulted from the alteration of corundum. 



b. In some specimens which I have received since the publication of 

 my first paper on corundum, I have observed that the coarsely-bladed 

 crystalline masses of cyanite from Wilkes county, N. C, resulting from 

 the alteration of corundum, are further changed into micaceous minerals. 

 They are very finely granular, scaly, and show the bladed structure and 

 cleavage of the original cyanite, and between the laminae minute scales 

 of mica and a little quartz. 



They have a grayish to brownish-white color, faint pearly lustre. H =^ 



2.5. sp. gr. =- 2.920. The purest material has been analyzed by my son, 

 Mr. F. A. Genth, Jr., who found : 



SiO^ — 35.58 



AI2O3 = 49.42. 



' Fe^Oj = trace 



MgO = trace 



CaO — 6.84 



Na^O = 2.11 



K2O = 3.01 



H.,0 = 4.12 



100.58 

 This analysis would correspond to about 59 % of calcium-sodium -mica 

 (margarite), 29 % of potassium mica (muscovate), 9.7 % of unaltered 

 cyanite and about 2.6 % of quartz. 



7. 'When loere the Corundum Alterations formed ? 



In many of the gravel beds in the Southern States, especially in North 

 Carolina and Georgia, corundum is frequently met with, very i-arely asso- 

 ciated with diamonds, but generally with gold, zircon, monazite, xenotime, 

 brookite, octahedrite, rutile, menaccanite, chromite, magnetite, cyanite, 

 garnet, epidote, »&c. 



The corundum is sometimes, but rarely found in crystals of the usual 

 form, mostly in fragments and cleavage pieces with very sharp edges and 

 angles, which hardly ever are water-worn. These fragments show that the 

 •minerals have been broken by a very great force which had acted upon 

 them very rapidly. Many of these fragments give evidence that, at the time 

 when the corundum was broken up, a great portion of it had already under- 

 gone an alteration into other minerals. The most frequent are muscovite, 

 mostly in fine scales, sometimes in subfibrous coatings ; some also show 

 feldspar, margarite, black spinel and tourmaline, and very rarely cyanite , 

 usually containing a nucleus of corundum. The altered minerals, accord- 



