230 Pen field and Pratt — Occurrence of 



optical examination, and in a letter to Nordenskiold he states* 

 that the material was found to be practically homogeneous, 

 uniaxial and with negative double refraction, but whether 

 hexagonal or tetragonal could not be determined. The uni- 

 axial material which Bertrand had taken for calcite was in 

 reality thaumasite, and Bertrand in a letter to Nordenskioldf 

 withdrew his objection. He gives also the approximate 

 indices of refraction to — 1*503, £ = 1467, which differ from 

 those of calcite. 



In 1890 WidmanJ described specimens of thaumasite 

 belonging to the mineral collection of the University of 

 Upsala, which are reported to have been found at Kjdlland, 

 about thirteen miles from the original locality Areskuta, and 

 two analyses by Hedstrom quoted by him agree very closely 

 with the ones made by Lindstrom. From Hedstrom's analy- 

 ses the formula CaSi0 3 , CaC0 3 , CaS0 4 , 15H 2 was derived, 

 and as pointed out by Widman this slight change in the 

 formula agrees satisfactorily with the analytical results of Lind- 

 strom, who really had found over fourteen and one-half mole- 

 cules of water. 



It is with pleasure that the authors are able to announce 

 the discovery of this unusually interesting mineral at Burger's 

 quarry, West Paterson, New Jersey, the material having been 

 first brought to our notice by Mr. Geo. L. English, of New 

 York, who sent a specimen of it to the mineralogical labora- 

 tory of the Sheffield Scientific School for identification. The 

 mineral occurs as an aggregate of prismatic crystals, sometimes 

 so loosely held together that the individuals can be separated 

 by crushing between the fingers, while more often the masses 

 are firm and have somewhat the appearance of white alabaster. 

 Occasionally distinct prismatic crystals were observed, aver- 

 aging 0*5 mm in diameter and 2 to 4 mm in length, but they were 

 poorly formed and without distinct terminations. Some of 

 the masses showing fine prismatic crystals have a decidedly 

 silky luster. There is a distinct prismatic cleavage. Measure- 

 ments were only possible in the prismatic zone and approximated 

 to 60°, which determine the crystallization as hexagonal. On 

 examining fragments imbedded in Canada balsam ones can 

 readily be found which show a uniaxial interference figure 

 with negative double refraction. Using a polished plate, the 

 index of refraction for the ordinary ray was determined by 

 means of total reflection in a-mono-bromnaphthalene and found 

 to be 1*5125 for yellow Na. By means of a prism of 32° 58' 

 the following values were also obtained for yellow, co= 1*519 



*Geol. For. Forhandl., Stockholm, vol. ix, p. 35, 1887. 

 f Ibid., vol. ix, p. 131, 1887. 

 jlbid., vol. xii, p. 20, 1890. 



