Glauconite

glauconite

glaucophane

dolomite

siderite

Images

Formula:(K,Na)(Mg,Fe2+,Fe3+)(Fe3+,Al)(Si,Al)4O10(OH)2
Phyllosilicate (sheet silicate), 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

Sedimentary 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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