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1909-10.] The Chemistry of Submarine Clauconite. 
It will be observed that the composition of glauconite is subject to small 
variations, especially in the alumina, magnesia, and ferrous iron.* On the 
whole, however, the general composition of glauconite may now be con- 
sidered to be firmly established. If we regard A1 2 0 3 as replacing Fe 2 0 3 , 
and CaO, MgO, and FeO as replacing K 2 0, the formula KFeSi 2 0 6 .H 2 0 agrees 
tolerably well with these analyses.]* 
To return to the colloidal suspension of glauconite, the formation of 
such a suspension is calculated to raise some doubts as to whether glauconite 
is really a crystalline and not rather a colloidal substance. The suspensions, 
whether prepared from granular or from purified glauconite, behave exactly 
like clay suspensions. Within a week or so they gradually deposit much 
of their load in progressively finer particles ; but ultimately a true colloidal 
solution remains. This latter is transparent, opalescent, yellow by trans- 
mitted and green by reflected light, and is stable for months unless 
coagulated by a trace of acid or by a considerable addition of some neutral 
or alkaline electrolyte. It contains about 1J gr. of glauconite per litre. 
Examined microscopically, flocculent glauconite presents the appearance 
of rounded particles, varying somewhat in size, with no suggestion whatever 
of crystalline outlines. A small proportion of the particles, especially the 
larger ones, retain the characteristic birefringence of granular glauconite. 
It is worthy of note that flocculent glauconite absorbs dyes ( e.g . methylene 
blue) quite as greedily as clay. 
II. Organic Matter in Glauconite. 
When glauconite grains are made to yield a colloidal suspension by 
the method described above, it is evident that they undergo a drastic 
* The determination of ferrous iron, which, in presence of organic matter, is the 
mineralogical chemist’s despair, was carried out with special precautions in the present 
analyses, as follows : — One or two gr. of material are placed in a large platinum crucible 
with 15 cc. of 20 per cent, sulphuric acid and about 1 cc. of strong hydrofluoric acid. The 
crucible is closed off by a leaden block having two leaden tubulures, through which a 
current of carbon dioxide is sent through the apparatus. After 15 minutes’ gentle 
boiling, the glauconite is dissolved, and the crucible is allowed to cool in carbon dioxide. 
The contents are transferred to a measuring-flask, made up to 50 cc., and allowed to stand 
in an atmosphere of carbon dioxide for 5-6 hours, by which time the organic matter will 
have settled to the bottom. An aliquot portion of the clear liquor is then pipetted off and 
titrated with permanganate. Organic matter would seriously impair the accuracy of this 
determination only in so far as it went into solution in dilute acid at boiling temperature ; 
in the case of glauconite there does not seem to be much danger from this source. 
t Clarke ( U.S . Geol. Survey Mon., xliii. p. 243, 1903) arrives at the same formula, 
KSiFe 2 0 6 , from a consideration of the older analyses, but leaves water of hydration out 
of account on the ground that it is “ zeolitic.” As a matter of fact, glauconite can take up 
several molecules of “ zeolitic ” water, but the one molecule which persists in the sharply 
dried mineral would rather seem to be water of constitution. 
