574 
M. DES CLOIZEAUX ON AMBLYGONITE AND MONTEBEASITE. 
respect to the Amblvgonite from the State of Maine, nor with that from Montebras, the 
analysis of which has been made by Pisani ; since, as the pyrognostic characters led 
one to foresee, these differ from the Amblygonites of Saxony and Montebras (which I 
had previously named Montebrasite) by the absence of soda, by the preponderance of 
lithia, and by the presence of a notable amount of water, while at the same time the 
minerals resemble one another in their almost equal proportions of phosphoric acid and 
of alumina. 
If we leave the water out of the question, the soda seems here to play the part which 
I have attributed to it in certain pseudo dimorphous bodies, and especially in the sulphate 
of potash* ; except that Amblygonite and Montebrasite belong to the same crystalline 
system, and their optical characters alone present complete incompatibility, while the 
crystals of sulphate of potash occur in two nearly resembling but incompatible types, 
according as they do or do not contain soda. 
It results from what has been above stated, that the differences which Amblygonite 
and Montebrasite present in their physical and chemical characters appear to be 
sufficiently decided^ to compel us to treat these substances as belonging to nearly related 
but distinct species — the one anhydrous, the other hydrated. We shall retain the name 
Amblygonite for the sodiolithic species first discovered at Penig by Breithaupt, and 
accordingly the white or violet-tinted lamellar masses abundant at Montebras will be 
included under it J ; while the hydrated and entirely lithic species, comprising the 
beautiful laminar specimens and the crystals from Maine, as well as some greenish 
masses from Montebras, still very rare, will be embraced under the name Montebrasite, 
which I had at first proposed for the first masses from Montebras, an erroneous analysis of 
s 
which had been furnished, as before mentioned, by the laboratory at the Ecole des Mines. 
In the following pages I shall give a detailed description of the principal crystallo- 
graphic and optical characters, as well as the analyses of the two species. 
I. Anhydrous Sodiolithic Species — Amblygonite. 
The Amblygonite of Montebras, designated as Montebrasite in my communication to 
the Academy of Sciences of Nov. 27, 1871, has only been met with in laminar masses, 
sometimes opaque and of a dull white, sometimes more or less translucid, and in parts 
even transparent and with a faint tinge of violet. These masses exhibit only two 
* “ Memoire sur pseudodimorphisme de quelques composes naturels et artificiels,” Annates de Chimie et de 
Physique, 4 me ser. tom. i. p. 313. 
t I would further remark, as a distinctive feature of secondary importance, that the Montebrasite (the 
former Amblygonite) from the United States and that from Montebras present at least three distinct cleavages, 
parallel to the faces of an oblique-angled parallelepiped ; while on none of the specimens of Amblygonite (the 
former Montebrasite), so many of which have passed through my hands, have I ever been able to detect more 
than two cleavages. 
+ These are the masses which are designated as Montebrasite in my notice in the £ Comptes Rendus ’ of 
27 Nov. 1871, whereas the greenish specimen from Montebras is described as Amblygonite. I propose this 
inversion of the names out of respect to the priority of the name Amblygonite. 
