Penfield and Ford — Stibiotantalite. 61 



Art. X. — On Stibiotantalite; by S. L. Penfield and W. E. 



Ford. 



Historical. — Stibiotantalite was first described by G. A. 

 Goyder* in 1892 and more minutely in 1893, as occurring in 

 rounded water-worn fragments in the tin-bearing sands of 

 Greenbushes, West Australia. No crystals were observed, but 

 it was evident from the cleavage of the material and its action 

 on polarized light that it possessed a crystalline structure, and 

 it was assumed that it belonged to the orthorhombic system, 

 though no convincing evidence was brought forth. An analy- 

 sis, which is quoted later in this article, indicated that the min- 

 eral is essentially a combination of oxides of antimony and 

 tantalum, with some niobium and a very little bismuth, but no 

 formula was suggested. The physical properties were given as 

 follows: — Hardness, 5 to 5*5. Specific gravity, 7*37. Luster, 

 adamantine to resinous. Color, pale reddish-yellow to green- 

 ish-yellow. Fracture, subconchoidal to granular. Within the 

 past few years a considerable quantity of this material has 

 become available to collectors through the agency of several 

 mineral dealers. 



Crystals from Mesa Grande, San Diego County, California t a 

 New Locality. 



The material from Mesa Grande was brought to the atten- 

 tion-of the present writers by Mr. Ernest Schernikow of .New 

 York. It was observed by him as occurring very sparingly 

 with the wonderful tourmaline crystals found at the locality 

 and described by Sterrett,f and great pains were taken to have 

 every crystal and fragment carefully saved. In all, some 

 twenty-five crystals have been found, representing several years 

 savings from a vast amount of material, so it may be considered 

 a rare mineral at the locality. Associated with it, besides the 

 tourmaline already referred to, are large and wonderfully 

 beautiful crystals of pink beryl of unusual habit, fine crystals 

 of quartz, orthoclase and lepidolite, and, as a great rarity, cas- 

 siterite. The orthoclase is generally kaolinized to a considera- 

 ble extent. Several crystals of stibiotantalite were observed 

 grown on to, or over, pink tourmaline ; one group has attached 

 to it a little feldspar and lepidolite ; the others are all detached 

 crystals and some of them are doubly terminated. None of 

 the detached crystals show fresh fractures, and they evidently 

 were found loose in the deposit. Stibiotantalite appears to be 



* Proceedings Chem. Soc, 1892, 9, p. 184. Journal Chem. Soc, 1893, lxiii, 

 p. 1076. 



f This Journal (4), xvii, p. 459, 1904. 



