Glauconite from the Precambrian Belt Series, Montana.
Glauconite from the upper part of the Missoula Group of the Belt Series, Flathead County, Montana, has been dated at 1070 million years by potassium-argon and rubidium-strontium analyses. This is the first glauconite of Precambrian age reported in North America.
Gulbrandsen
R A
RA
Goldich
S S
SS
Thomas
H H
HH