Various potassium silicates-leucite, feldspar, sericite, and glauconite-and the potassium sulphate, alunite, have received attention and certain of them have been utilized to a small extent, but none of them are normally able to compete on the market.
"The Economic Aspect of Geology"
C. K. Leith
The magnesia and potash are, also, largely restored from the ocean; the former in dolomites and magnesian limestones; the latter in glauconite sands.
"The Birth-Time of the World and Other Scientific Essays"
J. (John) Joly
The green colour, on close inspection, is seen to be due to the presence of innumerable small green grains of a mineral called glauconite.
"Sea-Weeds, Shells and Fossils"
Peter Gray B. B. Woodward