148 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 58. 



Analyses and ratios of Jiydrotalcite. 



Constituents. 



Per cent. Per cent. 



SiOj 

 Al/J. 

 Fe^O; 

 CaO , 

 MgO 

 PeO. 

 CO2. 

 H,0. 



0.44 



15. 32 



1.89 



None. 



39.72 



.28 



7.60 



35.46 



100. 71 



17.60 



40.40 

 7.60 



1.00 



1.07 

 12.4 



1X1.00 



6X1.00 



1X1. 07 

 12X1.03 



This leads to the formula 6MgO.AL03.CO,.12H30 or MgCOa.SMg 

 (OH)2.2Al(OH)3.4H20. 



Pyrognostics. — Before the blowpipe the mineral glows with intense 

 light, but does not fuse, and becomes silvery white. Heated in a 

 closed tube it decrepitates, gives abundant water, and turns silvery 

 white. It is easil}^ soluble in acids, leaving a slight residue. 



The mineral houghite described by C. U. Shepard from St. Law- 

 rence County, NcAV York, is probably hydrotalcite, as pointed out by 

 J. D, Dana. In appearance it is very similar to the hydrotalcite from 

 Norway. Under the microscope it shows a weak birefringence and 

 an index of refraction of about 1.510. The material is considerably 

 intermixed with spinel and other minerals, so that a chemical analysis 

 would lead to no definite results. The analyses by Johnson, there- 

 fore, ran mean but little. The mineral is derived from spinel. 



Petterd, Cat. of the Minerals of Tasmania, p. 1G7, 1910. 

 Ward, Cat. of the Minerals of Tasmai ia, p. 1G9, 1910. 

 Hezner, Centralbl. f. Min., etc., p. 18, 1912. 

 HiMMELBAUER, Tsch. Min. u. Pet. Mitth., vol. 31, p. 32, 1912. 

 Tasmanian Dept. of Mines, Geol. Surv. Record No. 2, 1914. 



This mineral was described by Petterd first as kammererite and 

 later as a new mineral. It occurs in irregular masses, veins, and 

 blebs in a yellowish green serpentine, near the Adelaide Mine at 

 Dundas, Tasmania. The color is lilac weathering to brown. It is 

 foliated in character and has an oily luster. Under the microscope 

 the mineral shows a fibrous structure radially disposed about nuclei 

 of chromite. The two analyses of the mineral are widely divergent 

 and lead to quite different ratios. In neither case is there any men- 

 tion of the homogeneity of the material analyzed as determined 

 under the petrographical microscope. These analyses are given 

 below. 



