582 
M. DES CLOIZEAUX OX AMBLYGOXITE AND MONTEBEASITE. 
Amblygonite of Montebras. 
.A 
Amblygonite of Penig, 
r 
Pisani. 
Kobell. 
A 
Kammelsbei-g. 
Kammelsbei-g. 
Eluorine 
8-20 
9-00 
10-06 
9-44 
Phosphoric acid 
46-15 
45-91 
48-55 
48-00 
Alumina 
. . . . 36-32 
35-50 
36-36 
36-26 
Lithia 
8-10 
6-70 
7-96 
6-68 
Soda 
2-58 
5-30 
0-93 
3-29 
Potash 
.... 
0-40 
0-43 
Time . 
0-50 
Oxide of manganese. . 0-40 
.... 
.... 
Loss on ignition 
1-10 
0-70 
.... 
.... 
Silica mixture . . 

0-60 
— 
102-85 
104-21 
104-26 
104-10 
Density 
, 3-09 to 3-10 
.... 
.... 
3-11 
II. The Hydrated Litliic Species — Montebrasite. 
I received quite recently (November 1871) from M. Moissenet a new specimen obtained 
from the mine of Montebras, from the midst of the masses which I had at first called 
Montebrasite (now Amblygonite), and distinguishable by its possessing- an unwonted 
transparency rare in that substance. A cursory examination sufficed to show that I 
had not to deal in it with the old Montebrasite (i. e. Amblygonite), but rather with the 
mineral supposed to be Amblygonite, although then not analyzed, and of which the 
finest specimens, which presented the form of laminar masses or of coarse crystals *, 
had been found hitherto at Hebron, State of Maine, U.S. A. 
The new specimen from Montebras is of a pale green colour in its more transparent 
parts, and presents the three principal cleavages p , m, t which I have recognized in the 
masses from Hebron, and of which the first is easily obtained, and yields an unbroken 
surface with a somewhat pearly lustre, while the second, less easily obtained, results in 
broken surfaces vitreous in lustre ; and the third is a still more difficult cleavage, and is 
recognizable by small reflecting surfaces scattered among rough surfaces of fracture. 
- * In the 5th edition of his ‘ System of Mineralogy,’ p. 545, Mr. Dana has figured a large crystal of Monte- 
brasite of Hebron, the forms of which, referred to the oblique-angled parallelepiped produced by the three 
principal cleavages p, to, t, and which I adopted in 1863 as the primitive form of amblygonite, now Monte- 
brasite, seem as if they ought to be expressed by the simple symbols to, t, g 1 , g l , x= d g l ). Unfortunately 
the measure indicated by Mr. Dana could only be approximately made in consequence of the inequalities of the 
surface of the crystal, and would not justify our using them as means of determining with exactitude the 
dimensions of the primitive solid. 
Thus if we take for the fundamental data the numbers to t = 135° 30', p m — 10b°,p t forwards =88° 30' 
(exact measures taken on planes of cleavage), t g' adjac.— 73° 20', to c adjac. = 131° 50' (approximate measures 
obtained on the crystals), we obtain for the forms g 4 and x=(d f^g 1 ), by calculation, incidences so far divergent 
from those obtained by observation, namely a difference of from 3° to 4°, that it would be better to wait for 
fresh observations made upon more perfect crystals. Agreement between the results of calculation and direct 
measurement is only to be obtained by having recourse to symbols for which the expressions are .so complicated 
as to be altogether unusual in the triclinic system. 
