360 Brush and Dana—Fairfield County Minerals. 
incipient alteration. “ is generally foliated to lamellar, although 
sometimes of a somewhat radiated structure. The second 
variety (B) occurs in masses of considerable size interpenetrated 
rather irregularly with se and quite uniformly run through 
with thin seams and li of a black manganesian mineral of 
not very clearly Satned as. This mineral is granular in 
texture, lustrous, is difficultly fusible, and consists for the most 
part of the hydrated oxides of manganese at iron; but con- 
tains also phosphoric acid and traces of lim 
This second variety of fairfieldite is often friable to the 
touch and lacks something of the brilliant luster of the first 
variety. It also shows oieater difference of sonar passing 
rom the distinct melanie to the massive and radiated form. 
form could be clearly made out, but exact measurements were 
quite impossible ; this is ati more to be regretted as the number 
of variable elements is so large. The cleavage parallel to 6 
rete is highly perfect that parallel to a (100) somewhat less 
The erystals belong to the Trichinic System, and the general 
habit is shown in the adjoining figure. The following supple- 
ment angles were accepted as the basis of the calculations. 
Aac 100.001 = 88° 
aab 100.010 = 102° 
aap 100.111 = 56° 30’ 
Cap QOL, 111 = 33 
bp} 010,111 = 18° 30’ 
these angles, the lengths and mutual 
Fro 
iaiieations of the axes were calculated, as 
follow 
¢ (vert.) b a 
"706 35757 1-0000 or 
"1976 1-0000 “2797 
Also a (cd) B (cra) y(b.4) 
102° 9’ 94° 337 77° 20° 
The observed planes are as follows :— 
