Professor Breithaupt on Achmite, and Hyalosiderite. 868 



in the magnitude of the lateral edges mentioned by Mitscherlich. 

 The inclinations of both lateral cleavages, I found to be essen- 

 tially the same as those which the latest measurements give of 

 Augite. The specific gravity = 3.3820. It differs from Augite 

 in being rather softer, much more easily frangible, and in having 

 much less lustre on the compact fracture. It comes nearest in 

 these characters to the Hedenbergite of Berzelius, which is also 

 but a variety of Augite. These appearances alone are sufficient 

 to shew, that the mineral is no more in a fresh condition, on the 

 contrary, has undergone some change. In this way, we can ex- 

 plain the difference in chemical composition observed in Augite, 

 but not of that change by which out of Augite green earth is 

 formed. As Professor Mitscherlich states the specific gravity 

 at 3 2, it is probable that the specimens he examined were more 

 decayed than those I employed. It is also possible that the po- 

 sition of the planes of crystallization may have been altered by 

 decomposition. 



II. Hyalosiderite. 



Professor Walchner has given a very accurate mineralogical 

 description, and also a chemical analysis of this mineral in 

 Schweigger''s New Journal, b. ix. h. i. s. 63-80. Its locality is 

 that remarkable conical hill, named Kaiserstuhl, in Baden, 

 which is composed of members of the secondary trap series. At 

 first sight, it might pass for a new mineral ; but Professor Walch- 

 ner communicated to me his doubts as to its being a new species, 

 and remarked, that it was probably only a variety of Olivine. On 

 examining some specimens, I found that it bore the same relation 

 to Chrysolite that Achmite does to Augite, viz. having an inferior 

 hardness, and very low lustre in the compact fractured surface. 

 Measurement proved, that the Hyalosiderite is a variety of Chry- 

 solite^ but in a state of partial decomposition. This decomposed 

 condition, explains the difference in chemical composition from 

 Chrysolite. It is worthy of remark, that, when a mineral is altered 

 by weathering, that the open cleavages remained but little af- 

 fected. This is most striking with the felspar family, as in Or- 

 thoklase, which, when so much decomposed as to be easily pressed 

 into a kind of porcelain earth between the fingers, yet retains its 

 most obvious cleavages. But it is without lustre in the direction 

 of the compact fracture. M. Kiihn, inspector of the Royal Por- 



