RE-EXAMINATION OF AMERICAN MINERALS. 135 



The composition of this mineral is interesting, as it furnishes 

 the only example in the mineral kingdom of the isomorphism 

 of copper and cobalt, where the latter may be replaced to a 

 greater or less extent by the former. Among artificial pro- 

 ducts exhibiting this replacement, we have the cupro-sulphate 

 of cobalt with 10 and with 7 atoms of water, the latter crystal- 

 lizing in oblique prisms, like the sulphate of cobalt with the 

 same number of atoms of water, which is also the form of green 



vitriol. 



29. Thallite, identical with Saponite. 



This mineral was originally described by Dr. D. D. Owen,* 

 by whom it was found on the north shore of Lake Superior, 

 diffused in the amygdaloidai traps of that locality. At the 

 time it was first noticed it was supposed to contain a new 

 element, which was called thallium ; the mineral itself was 

 named thallite. Through the kindness of Dr. Owen we were 

 furnished with some of the mineral, which was subjected to 

 most careful analysis, the result showing nothing in its com- 

 position by which it differs from saponite ; and all attempts to 

 isolate a new earth from it were vain. A second portion 

 of the thallite with some of the supposed thallia was sent us 

 by Dr. Genth, of Philadelphia, which was labeled " not quite 

 pure ;" its composition, however, differed from the first prin- 

 cipally in containing less water, as it was allowed to dry for a 

 greater length of time — it being a common thing for saponites 

 to lose more or less of their water by desiccation in the air. 



The result of the examination of the thallite was given in a 

 note in the last number of the American Journal of Science 

 and Arts. Many of the reactions contained in the original 

 description of thallite and thallia we have been unable to recog- 

 nize, among them the evolution of chlorine by the action of 

 hydrochloric acid, and the precipitation by a neutral solution 

 of succinate of ammonia. The pea-green color of the concen- 

 trated hydrochloric acid solution of the thallia, prepared in the 

 way mentioned by Dr. Owen, is easily explained by the presence 

 of an exceedingly minute quantity of the chloride of chromium, 

 as the smallest trace of this last metal will, under the circum- 

 stances, produce that color. The results of our analyses are as 

 follows : 



* Jour. Acad. Nat. Sci. Phila., ii, part 2d, 1852. 



