Glauconite

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Glauconite

Glauconite is a phyllosilicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
(mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic with a tendency towards pseudo-hexagonal crystals and are similar in chemical composition....
group) mineral

Mineral

A mineral is a naturally occurring solid formed through Geology processes that has a characteristic chemical composition, a highly ordered atomic structure, and specific physical properties....
.

It can also be referred to as an iron silicate. It crystallizes with monoclinic geometry. The name is derived from the Greek

Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
glaucos (??a????) meaning 'gleaming' or 'silvery', to describe the appearance of the blue-green color, presumably relating to the sheen and blue-green color of the sea's surface. Its color ranges from olive green, black green to bluish green.

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Encyclopedia

Glauconite is a phyllosilicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, comprising approximately 90 percent of the crust of the Earth....
(mica

Mica

Mineral

Greek language

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. Iron is a Group 8 element and period 4 element. Iron is lustrous and silvery in color....
content of the mineral. In the Mohs scale it has hardness of 2. The relative specific gravity

Specific gravity

Specific gravity is defined as the ratio of the density of a given solid or liquid substance to the density of water at a specific temperature and pressure, typically at 4?C and , making it a dimensionless quantity ....
range is 2.4 - 2.95. It is normally found in dark green rounded nodules of sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.As the term is used by geologists, sand particles range in diameter from 0.0625 to 2 millimeters....
size dimension. It can be confused with chlorite

Chlorite group

The chlorites are a group of Silicate minerals minerals. Chlorites can be described by the following four Solid solution based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn....
or with some clay

Clay

Clay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired....
s.

Normally, glauconite is considered diagnostic of continental shelf

Continental shelf

The continental shelf is the extended perimeter of each continent and associated coastal plain, and was part of the continent during the glacial periods, but is undersea during Ice age such as the current epoch by relatively shallow seas and Bay....
marine depositional environments

Sedimentary depositional environment

In geology, sedimentary depositional environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record....
with slow rates of accumulation. Typically, it appears in Jurassic

Jurassic

The Jurassic is a geologic period that extends from about annum to Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
/lower Cretaceous

Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
deposits of greensand

Greensand

Greensand is an olive-green coloured sandstone Rock which is commonly found in narrow bands, particularly associated with bands of chalk and clay worldwide; it has been deposited in Marine environments at various times during Earth history, such as during the Jurassic and Cretaceous Geologic time scale....
, so-called after the coloration provided by the glauconite. It can also be found in impure limestones and in chalk

Chalk

Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. It forms under relatively deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
. It develops as a consequence of diagenetic

Diagenesis

In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration and metamorphism....
alteration of sedimentary deposits, changes in the biotite

Biotite

Biotite is a common Silicate minerals#Phyllosilicates mineral within the mica group, with the approximate chemical formula K3AlSi3O102....
micas, for example, being influenced by the decaying process of the organic matter in animal shells. Glauconite forms under reducing conditions in sediments and such deposits are commonly found in nearshore sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock Particle size . Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust ....
s, open oceans and the Mediterranean Sea

Mediterranean Sea

The Mediterranean Sea is a sea or Ocean off the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Europe, on the south by Africa, and on the east by Asia....
but not in the Black Sea

Black Sea

The Black Sea is an inland sea sea bounded by southeastern Europe, the Caucasus and the Anatolia and is ultimately connected to the Atlantic Ocean via the Mediterranean Sea and Aegean Seas and various straits....
or in fresh-water lakes. It oxidises

Redox

Redox describes all chemical reactions in which atoms have their oxidation number changed.This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane , or it can be a complex process such as the oxidation of sugar in the human body through a ser...
on contact with air.

Glauconite has long been used in Europe as an artistic oil paint, especially in Russian "icon

Icon

An 'icon' is a religious work of art, most commonly a painting, from Eastern Christianity. More broadly the term is used in a wide number of contexts for an image, picture, or representation; it is a sign or likeness that stands for an object by signifying or representing it either concretely or by analogy, as in semiotics; by extension, ...
paintings". It is found as a pigment in wall paintings from Roman Gaul

Roman Gaul

Roman Gaul consisted of an area of provincial rule in the Roman Empire, in modern day France, Belgium, Luxembourg, and western Germany. Roman control of the area lasted for 600 years....
.

The wide distribution of these sandy deposits was first made known by naturalists on board H.M.S. Challenger, in the expedition of 1872-1876.