M. DES CLOIZEAUX ON AMBLYGONITE AND MONTEBEASITE. 
585 
Note upon Wavellite of Montebr as. 
Wavellite, in the form of thin coatings, presenting a mammillated and fibrous 
structure, forms a layer over almost all the fissures that occur in the Amblygonite of 
Montebras ; and sometimes even the latter is seen to lose its laminar structure, to 
become white and opaque, and to pass insensibly into the former mineral. When 
the coatings are somewhat thick and contain cavities, radiated spherules are found in 
them, which are composed of long thin needles with brilliant terminations. These 
needles exhibit a vertical prism that is deeply grooved but cannot be measured ; its 
acute edges are truncated by the diagonal face f, and surmounted by a rhomboidal 
octahedron, two culminating edges of which are replaced by minute faces of the bevel 
a 1 . Professor Miller, in his ‘Elementary Introduction to Mineralogy,’ has figured two 
solids of a similar kind, b k and e 3 , both of which are situated in the zone (f a x , like the 
terminal octahedron of the needles of Montebras ; but their angles of incidence do not 
at all agree with those that I have succeeded in measuring with some exactitude. 
Moreover, by adopting the fundamental crystallographic data of Professor Miller, the 
symbol of the new form will be e 8 , and the calculated angles, as compared with those 
resulting from direct measurement, are : — 
Calculated. 
=12332 
3 
g' e & upon e H = 56 28 
3 3" 
J e 8 e 8 upon a 1 = 112 56 
'33 
e\ a 1 =146 8 
3 
e 8 e 8 upon g 1 =120 22 
V. 3 3" 
Observed. 
123 ' to 123 25. 
56 20 to 57 30. 
113 52 mean. 
147 approximate. 
121 mean. 
Most of the known analyses of Wavellite indicate the presence in it of a small 
quantity of fluorine, sometimes as much as two per cent. M. Pisani has ascertained 
that the variety from Montebras, formed in the midst of other fluoriferous phosphates oi 
alumina, contains : — 
Fluorine 2-27 
Phosphoric acid 34 - 30 
Alumina 38-25 
Water 26-60 
101-42 
Specific gravity . . . . 2-33 
