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Formula: (K,Na)(Mg,Fe2+,Fe3+)(Fe3+,Al)(Si,Al)4O10(OH)2
Phyllosilicate (sheet silicate),
dioctahedral mica group of the
mica group
Specific gravity: 2.4 to 2.95
Hardness: 2
Streak: Light green
Colour: Blue-green, yellow-green, green, rarely colourless
Solubility: Readily decomposed by hydrochloric acid
Common impurities: Ti,Ca,P
Environments
Glauconite, which forms only in a marine environment maintained in a reducing condition by bacterial action,
derives its magnesium and potassium from the sea water, and its other constituents from mud. Glauconite has
formed as a marine deposit in every geological age since the pre-Cambrian (4600 to 541 Ma) and is found in many modern
marine sediments.
Sedimentary glauconite most commonly occurs as rounded pellets from one to several millimeters in diameter, and
is commonly made up of an exceedingly
fine-grained, but obviously crystalline aggregates of overlapping crystal plates
(AM 26.683-708).
It occurs especially in loosely consolidated sandstone (greensand), and
impure limestone and
siltstone, associated with
quartz, feldspar,
glaucophane, dolomite,
siderite, calcite,
ankerite, pyrite and
limonite
(HOM).
Localities
Glauconite is of very widespread occurrence. Formation is presently taking place along many continental margins,
particularly along the margins of eastern and western United States, northern Spain, southern Japan, south western
Australia, eastern and south western Africa and the southern areas of South America
(Dana).
At the Francon quarry, Montréal, Quebec, Canada, a member of the glauconite series has been identified as black
stringers 2 to 3 mm long on a specimen of sill rock
(MinRec 37.1.35).
The first recorded locality for glauconite is the Klódka quarry, Skole, Lviv Oblast, Ukraine.
At the Bonne Terre Mining District, St. Francois county, Missouri, USA, glauconite occurs as crystalline grains in
dolomite
(Dana).
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