1921] NATURAL SCIENCES OF PHILADELPHIA 171 



The plumasite is a coarse allotriomorphic granular aggregate of 

 white oHgoclase (AbsAn,) in which are imbedded pale violet blue 

 idiomorphic crystals of corundum. Scaly films of margarite occur 

 in fractures in the corundum. One hundred feet northwest of 

 the corundiferous portion of the dike, the rock consists of coarse 

 granular plagioclase without corundum, but with occasional nests 

 of a grayish-green fibrous monoclinic amphibole. Twenty-five 

 feet southeast of the corundiferous portion, the dike consists of 

 microcrystahine and porphyritic andesine. An analysis of the oli- 

 goclase is given below. 



Italy: In 1903, Lacroix^ called attention to the occurrence of 

 plumasite near Mosso Santa Maria, Biella, Italy, from which Gon- 

 nard'^ had described corundum crystals. An analysis of the oligo- 

 clase is given below. 



New Caledonia: Subsequently, Romeu" noted the occurrence 

 of plumasite in New Caledonia. 



Transvaal: The Transvaal corundum deposits have been des- 

 cribed by Wagner. 12 South Africa is the leading corundum-pro- 

 ducing country at present, the greater part coming from the Zout- 

 spansberg and Pietersburg districts of the Transvaal. Most of the 

 corundum recovered occurs as alluvial crystals or fragments and 

 boulders. The source of the material was found to be a plumasite 

 composed essentially of andesine, (AbsjAn^s), greenish biotite 

 and corundum. The corundum occurs in crystals up to 6 inches 

 in length scattered through the plumasite, which, however, may 

 consist wholly of andesine. 



Natal: In 1919, Du Toit^^ described the plumasite of Natal, 

 with details concerning its relation to the country rock, and mode 

 of origin. 



The Natal plumasite forms dikes in the serpentine bodies of the 

 Tugela Valley. The area is underlain by hornblende-schists, 

 granuHtes, and basic gneisses, riddled with dikes and veins of peg- 

 matite and aplite. In this complex are sills of serpentine., a light 

 gray to dark green fine grained rock composed almost entirely of 

 antigorite, with occasional plates of talc and black particles of 



8 Univ. of Calif. Piibl., Dept. Geol., Bull. 3: 219-229, 1903. 



9 Bull. Soc. Franc. Min., 26: 147-150, 1903. 

 "Bull. S'^c. Franc. Min., 20: 177-181, 1897. 

 "Bull. Mus. d'Hist. Nat., 12: 594-596, 1906. 

 12 Trans. Geol. Soc. S. Africa, 21: 37-42, 1919. 

 " Trans. Geol. Soc. S. Africa, 21 : 53-73, 1919. 



