Glauconite
| Glauconite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (K, Na) (Fe 3+ , Al, Mg) 2 [(OH) 2 | (Si, Al) 4 O 10 ] |
|
Mineral class (and possibly department) |
Layered silicates (phyllosilicates) with mica sheets, composed of tetrahedral or octahedral nets |
|
System no. to Strunz and to Dana |
9.EC.15 ( 8th edition : VIII / H.13) 71.02.02a.05 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / m (No. 12) |
| Lattice parameters |
a = 5.246 Å ; b = 9.076 Å; c = 10.184 Å β = 101.1 ° |
| Formula units | Z = 2 |
| Physical Properties | |
| Mohs hardness | 2 |
| Density (g / cm 3 ) | 2.4 to 2.95 |
| Cleavage | perfectly |
| Break ; Tenacity | uneven |
| colour | yellowish green, green, blue green |
| Line color | light green |
| transparency | translucent |
| shine | Glass gloss, fat gloss, matt |
| Crystal optics | |
| Refractive indices |
n α = 1.590 to 1.612 n β = 1.609 to 1.643 n γ = 1.610 to 1.644 |
| Birefringence | δ = 0.020 to 0.032 |
| Optical character | biaxial negative |
| Axis angle | 2V = calculated: 20 ° to 24 ° |
Glauconite is a very common mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition (K, Na) (Fe 3+ , Al, Mg) 2 [(OH) 2 | (Si, Al) 4 O 10 ]. Structurally, glauconite belongs to the layered silicates ( phyllosilicates ).
Glauconite almost exclusively develops platy or massive to earthy mineral aggregates of green color, which can also play into yellowish or bluish tones.
Etymology and history
The mineral was named because of its color after the ancient Greek word γλαυκός glaukós with the posthomeric meaning “shiny”, “blue-green” or “blue-gray”. The original meaning of the word is probably derived from γλαῦξ glaúx or γλαύξ glaúx , genitive γλαυκός glaukós "owl", and should therefore mean "owl-shaped". The extent to which the different meanings are used in Homer is a point of contention in Classical Philology.
Glauconite was first described and named after its color in 1828 by the German mineralogist Christian Keferstein .
classification
Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the glauconite belonged to the department of "phyllosilicates", where together with brammallite , illite and wonesite it forms the group of "low-alkali mica" with the system no . VIII / H.13 within the mica group.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies glauconite in the category of "phyllosilicates". This, however, is further divided by the crystal structure , so that the mineral according to its construction in the subdivision "phyllosilicates (phyllosilicates) with mica panels composed of tetrahedral and octahedral networks" to find where it along with Aluminoseladonit , Boromuskovit , Chernykhit , Chromseladonit , Chromophyllite , ferriseladonite , ferroaluminoseladonite , ferroseladonite , ganterite , montdorite (Rd), muscovite , nanpingite , paragonite , phengite (mineral group), roscoelite , celadonite , tainiolite , tobelite , voloshinite the "muscovite group" with the system no. 9.EC.15 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also classifies glauconite into the “layered silicate minerals” section. Here it is in the " mica group (muscovite subgroup) " with system no. 71.02.02a can be found in the subsection “ Layered Silicates: Layers of six-membered rings with 2: 1 layers”.
Crystal structure
Glauconite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a = 5.246 Å ; b = 9.076 Å; c = 10.184 Å and β = 101.1 ° as well as two formula units per unit cell .
properties
Under the microscope, in contrast to other mica, glauconite does not appear in the form of layered packed crystals or flakes, but rather as rounded grains (pellets) in which the crystals do not have a preferred orientation. These are immediately noticeable because of their strong yellow to blue-green inherent color, which changes to brown when they begin to oxidize to limonite . Some of these pellets are assumed to originate from the excrement (excrement pills) of unknown marine organisms; but they can also be found as fillings in the chambers of foraminifera .
Education and Locations
Glauconite is formed by converting detritic biotite , illite or other starting materials such as feces from soil organisms in marine diagenesis in shallow water under reducing conditions. Direct precipitation from sea water is rare. Preferred educational establishments are sandstones and clay (also formation of green earth ) and limestone , often accompanied by phosphorites .
As a rather rare mineral formation, glauconite can sometimes be abundant at various sites, but overall it is not very common. Around 300 sites are known to date (as of 2014).
In Germany, glauconite was found near Würzburg in Bavaria, in the limestone quarries near Rüdersdorf near Berlin in Brandenburg, the "Emilie" mine near Peine in Lower Saxony, in the Neanderthal limestone quarry and in various quarries in the Sauerland in North Rhine-Westphalia as well as near Barmstedt , Lübeck- Moisling -Niendorf and Groß Pampau can be found in Schleswig-Holstein.
In Austria, the mineral was found in the quarry of the Wietersdort cement works in the municipality of Klein Sankt Paul and at the Fuchsofen near Dobranberg ( Kappel am Krappfeld ) in Carinthia, near Ernstbrunn in Lower Austria, in several places in Salzburg, in a quarry near Vils in Tyrol and near Weinzierlbruck ( Grieskirchen district ), St. Georgen an der Gusen and Plesching ( Urfahr-Umgebung district ) in Upper Austria.
In Switzerland, glauconite is known from a limestone quarry near Mellikon in the canton of Aargau and from Ängisort near Seedorf UR in the canton of Uri. In addition, glauconite is an important side issue in the deposits of the upper sea molasses in the foothills of the Alps. Glauconite-bearing sandstone was mined in quarries in the vicinity of Bern and found among others. a. Used in many buildings in the federal city. The typical gray-green colored stone therefore bears the name " Bernese Sandstone ".
Other sites are found in Egypt, the Antarctic, Australia, Belgium, Bolivia, China, Denmark, France, Georgia, Israel, Italy, Japan, Canada, Malta, Morocco, New Zealand, the Netherlands, Poland, Russia, Sweden, Slovakia , South Africa, the Czech Republic, Tunisia, Ukraine, Hungary, England in the United Kingdom and in many states of the USA.
Glauconite could also be detected in rock samples from the upper continental slope off the coast of New Jersey (USA) and from the Sad Ridge off the coast of the Japanese island of Honshū .
See also
literature
- Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 251 .
- Martin Okrusch, Siegfried Matthes: Mineralogy: An introduction to special mineralogy, petrology and deposit science . 7th edition. Springer Verlag, Berlin / Heidelberg / New York 2005, ISBN 3-540-23812-3 , pp. 287 .
Web links
- Mineral Atlas: Glauconite (Wiki)
Individual evidence
- ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 5th completely revised and supplemented edition. Weise, Munich 2008, ISBN 978-3-921656-70-9 .
- ↑ a b c Webmineral - Glauconite (English)
- ↑ a b c American-Mineralogist-Crystal-Structure-Database - Glauconite
- ↑ a b c Mindat - Glauconite (English)
- ↑ See Manu Leumann : Homreic words. Basel 1950.
- ↑ Dietrich Helling: clay and silt stones . In: Hans Füchtbauer (Ed.): Sediments and sedimentary rocks . 4th edition. Schweizerbart, Stuttgart 1988, ISBN 3-510-65138-3 , pp. 218-221 .
- ↑ Mindat - Number of localities for glauconite
- ↑ Franz Hofmann: Investigations in the subalpine and Mediterranean molasses of Eastern Switzerland . In: Eclogae Geologicae Helvetiae . tape 50 , no. 2 , 1957, p. 289-322 .
- ↑ a b List of places where glauconite was found in the [Mineralienatlas] and in Mindat