4 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
The analysis gave the results and ratios tabulated below: 
Analysis and ratios of leverrierite from Idaho. 
Sige be dae we eee 45.32 0.7516 75.16 1.003 
POOLE. |: 1 ies, eae 2.842124) 
7. 68 1.10X1 
BelOeri elo, . eweetananes 70,0044 < 
CHO 28 HOOD GL Saat bk 2.76 0492 
Meollat av ed. doilw pinion 16.0039 
5.60 1.12X} 
KO! Adit diiw Jinw..y-vsy, ai 12.0013 "i 
Nace G40 Pewee ie Seite 10.0016 
HO =aapsepien a, Cena 816  . 4529 
125.66  1.00X5 
nS AME GLO mek Moe ge ONO 1443. vn a * 
These ratios yield the formula: 
1/5 RO. OF 3Si0,. 5ELO. 
or expanded: 
RO. 5R.,03. 15Si0,.. . 25H,0. 
The miscellaneous bases may in all probability be safely assumed to 
replace the basic hydrogen, the simplified formula becoming 
Al,O,. 3510,. 5H,0. 
Obviously there must remain a considerable amount of uncertainty 
regarding the nature of this mineral, an uncertainty not cleared by 
the discussion by Wherry and Larsen.*? These authors add univalent 
and bivalent bases to the trivalent alumina, tentatively assuming 
that they occur as a replacement of this oxide. They show that the 
various minerals of the group vary in base (Al,0,+R’’O0+R’,0): 
silica ratio from 1:1.86 to 1:2.76. Unpublished investigations in 
this laboratory indicate a much wider range. To quote from the 
above authors ‘‘this variableness in composition within definite 
limits suggests that a mineral group is represented or at least a spe- 
cies including several subspecies, as is the case, for instance, with 
muscovite.”’ 
The leverrierite group of minerals is now being investigated here 
with especial reference to the bentonitic clays and any speculation 
now with reference to the constitution of the group would be prema- 
ture. Consequently it is deemed sufficient, for the present to record 
the properties and composition and mode of occurrence of the Idaho 
mineral. 
SERICITIC MUSCOVITE GOUGE FROM THE CARROLL-DRISCOLL MINE, 
BOISE BASIN, BOISE COUNTY, IDAHO. 
While sericite has for some years been recognized as an impor- 
tant mineral of metalliferous ore deposits and its mineralogical 
’ Esper S. Larsenand Edgar T. Wherry. Leverrierite from Colorado. Journ. Wash. Acad. Sci., vol. 7 
p. 208, 1917. 
