290 Chronicles of Science. | April, 
glistening particles of a metallic lustre, not unlike mica. It was 
unacted on by the blow-pipe, and contained no carbonaceous matter. 
Its composition was stated, at a meeting of the Geological Society 
of Glasgow, to be—Ferric oxide 90°5, Insoluble matter m HCl 
and NO, 9°5=100. This was, without doubt, a peculiar variety 
of micaceous iron ore. 
Dr. Tschermak’s “ Researches on the Group of Felspars,” 
referred to in our last number, have called forth a paper by 
Professor Rammelsberg, “On the Composition of Oligoclase and 
Labradorite, &.” (Ueber die Zusammensetzung von Oligoklas und 
Labrador, &.).* Although the different members of the felspar 
family consist of double silicates, which invariably contain one atom 
of protoxide to one atom of alumina ; or, in other words, in which 
the oxygen of the protoxide bears to that of the sesquioxide the 
constant ratio of 1:3, yet there probably exists no felspar which 
contains only a single protoxide, Thus in ordinary orthoclase- 
felspar, the potash is always accompanied by soda, which sometimes 
reaches so high a percentage that certain forms of sanadine or glassy 
felspar contain as much as one atom of soda to one of potash; and 
the same is the case with the orthoclase from the Norwegian zircon- 
syenite. These soda-bearing potash-felspars are probably to be 
regarded as regular associations of orthoclase and albite; such, at 
least, is certainly the case with the mineral called Perthite. Hxtend- 
ing this idea, Tschermak supposed that the existence of soda in all 
potash-felspars was referable to the presence of associated albite, as 
proved by analysis; but Rammelsberg objects that this is a point 
which can be determined, not by chemical analysis, but only by 
physical research ; and that this has hitherto failed to prove the 
existence of albite in such compounds. Thus, according to Ram- 
melsberg’s own analysis, the glassy felspar from the trachyte of the 
Drachenfels on the Rhine, contains 10°32 per cent. of potash, and 
3°42 of soda, corresponding to 57 per cent. of orthoclase and 43 of 
albite; the mineral thus consisting, according to ‘T'schermak’s 
theory, of one atom of albite and two of orthoclase: yet this mixed 
felspar, in which albite forms no less than one-third of the mass, m 
nowise differs, either in crystalline form or in optical properties, 
from the purest adularia. Such cases might, however, be explained 
by regarding the mineral as an isomorphous combination of potash- 
orthoclase with a soda-orthoclase unknown in an isolated form, 
but which evidently must be a monoclinic compound, and not a 
triclinic albite. 
Rammelsberg regards as equally inconclusive Tschermak’s ex- 
planation of the presence of potash in albite, and of potash and soda in 
anorthite ; physical observation having shown that orthoclase is not 
present in albite, nor othoclase and albite in anorthite. 
* «Poggendorifs Annaler,’ 1865. No. 9. 
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