Recoed of Geology of Texas, ISS'Z-ISQG. 
139 
Hidden, William Earl, and Mackintosh, J. B. 
“Fergusonite, mono-hydrated . — ^^Specific gravit.y=:5.67. Hardness 6 — 6.5, 
form tetragonal, wifcli acute octahedral terminations, a zirconoid plane 
hemihedrally developed .and, rarely, the basal pinacoid. The crystals are 
rough and dull gray exteriorly, but with a bronzy sub-metallic appearance 
on the- surface of fracture, which is small conchoidal and brilliant. Thin 
■splinters show a yellowish-brown translucence. Color, bronzy hair-brown. 
Streak and powder dull brown. It is infusible, but on ignition the pow- 
dered mineral changes to a pale olive-green color, and a momentary glow 
■creeps over the mass at the point of redness. iFragments decrepitate vio- 
lently when heated. With a microscope a peculiar light brown muddiness 
is noticed, and the mineral is filled with minute streaks and spots of a 
darker shade, all of which may indicate incipient alteration. 
“Crystals often have a thin coating of; or are otherwise partly altered to, 
the tri-hydrated variety next described. It is decomposed when in fine 
powder by hydrochloric acid, with separation of columbic acid. The ana- 
lytical results a;^ as follows: 
Cbs O 5 
46.27% 
86.30 
U O 3 
1.54 
1.59 
Th O 2 
3.38 
2.56 \ 
AI 2 O 3 
0.09 
0.27 J 
Fes O 3 
0.98 
Atomic weights, 
1.83/ 
(A) Ys O 3 * 
23.95 
110.55 
26.70[ 
(B) Ys O 3 * 
18.38 
113.3 
20.07 ) 52.65 
Pb 0 
1.43 
0.64/ 
Zn 0 
0.24 
0.30i 
Ca 0 
0.10 
0.181 
Mg 0 
0.04 
0.10/ 
IgnitiOQ Hs 0 
1.98 
11.00) 
110° C. Hs 0 

0.04 
V 15.79 
F 
0.91 
Atomic Ratio 
, 4 . 79 J 
99.33 
Less 0 — F 
0.38 
98.95 
*Total Ya O 3 , etc., and Ce earths=42.33.” 
“Fergusonite, tri-hydrated . — (Specific ,gravity=4.36 — 4.48, hardness about 
5. Color deep brown, almost black, thin edges show a yellowish-brown 
translucence. Form and exterior appearance same as the species pre- 
viously described. Streak and powder pale greenish-gray. On ignition 
turns light brown, but does not glow nor decrepitate like fergusonite. Is 
decomposed by hydrochloric acid with separation of columbic acid. 
