1866. | Mining, Mineralogy, and Metallurgy. 291 
Passing to the other felspars—Oligoclase, Labradorite, Andesine, 
&c.—the author agrees with Tschermak in regarding these different 
forms of soda-lime felspar as isomorphous compounds of anorthite 
and albite in definite proportions—a conclusion at which Ram- 
melsberg arrives by an elaborate tabulation of a very extensive 
series of analyses, and which is corroborated by certain crystallo- 
graphic considerations. 
At the conclusion of this paper we are reminded that the idea 
of regarding the middle terms of the felspar series as mixtures of 
the two extremes, is an idea which by no means originated with 
Tschermak, but which has been worked out in different ways by 
Waltershausen, Hermann, and others. 
To the same number of ‘ Poggendorff’s Annalen, Herr Schmid 
contributes three mineralogical papers. The object of the first of 
these is to correct the formula established by Von Kobell, for the 
hydrous silicate of lime called Okenite, and which is always expressed 
as 3 CaO, 4810,+6 HO. The author shows that one-sixth of 
the water present is simply hygroscopic, and may therefore be 
expelled at ordinary temperatures ; and that a second atom may be 
driven off at a higher temperature, and may hence be compared to 
“water of crystallization ;” the remaining four atoms being true 
“ water of combination,” essential to the constitution of the mineral. 
These three conditions of Okenite may be thus represented :— 
(1.) 3Ca 0, 4Si0, + 6HO 
(2.) 3Ca 0, 4S8i0, +5 HO 
(3.) 3CaO, 4Si0, +4HO 
In the second paper, Herr Schmid describes the aragonite from 
the Zechstem of Kammsdorf, near Saalfeld in Thuringia. The 
mineral occurs in small bundles of diverging crystals, locally called 
“needle spar” (Nadelspath); the crystals often presenting twin 
forms, and when colourless consisting simply of carbonate of lime 
with the merest trace of magnesia. ‘This aragonite is interesting as 
a dimorphic form of pure calcic carbonate, the entire absence of 
strontia and baryta—constituents commonly present in this mineral 
—having been determined by spectrum analysis. 
The examination of three varieties of psilomelane forms the 
subject of the third paper, and leads the author to adopt for this 
unsatisfactory species the formula of (MnO, BaO), 4 MnO, + 6 HO. 
Dr. F. Wibel has written an interesting paper on “ The Altera- 
tion-Products of Ancient Bronzes: a Contribution to the Origin of 
certain Copper Ores, especially the Red Oxide” (“ Die Umwandlungs- 
Produkte alter Bronzen: ein Beitrag zur Genesis emiger Kupfererze 
insbesondere des Kupferoxyduls”).} The green coating of cupreoug 
* ‘Ueber Okenit;’ ‘Ueber den Aragonit von Gross-Kammsdorf bei Saal- 
feld;’ and ‘ Ueber Psilomelan.’ 
+ ‘Jahrbuch fiir Mineralogie,’ &c., 1865. 4 Heft. 
