Nontronite

• Chloropal

• Na0, 3 ( Fe3 ) 2 (Si, Al) 4O10 (OH) 2 · nH2O
• Fe3 2 [( OH) 2 | (Si, Al) 4O10 ] NA0 · 3 ( H 2 O) 4
• ( Ca0, 5, Na) 0.3 Fe3 2 (Si, Al) 4O10 (OH) 2 * nH2O

Nontronite is a mineral from the mineral class of " silicates and Germanates ", which may be abundant in various localities in part, but overall is not widespread.

The mineral is crystallized in the monoclinic crystal system with the chemical composition NA0, 3 ( Fe 3 ) 2 ( Si, Al ) 4O10 (OH) 2 · nH2O, that is a complex composite layer silicate from the forming part of the clay minerals the smectite group.

Nontronite is usually cryptocrystalline and develops only rarely visible under the microscope crystals with pseudohexagonalem, blättigem habit. He usually can be found in the form wormlike, radialstrahliger to Globular graphite, net-like or felted mineral aggregates. Its color varies depending on foreign admixtures and impurities between light yellow and olive green to green. However, it also occurs in orange and brown color. His stroke color by contrast, is greenish white.

Etymology and history

The mineral nontronite was named after Nontron, a small town in the north of the Dordogne. However, the actual type locality is located at Le Mandereau in the municipality of Saint- Pardoux- la -Rivière. Here the nontronite was discovered in the degradation of manganese ( manganese dioxide).

Nontronite is called because of its color and its occurrence as Chloropal. Another synonym is the Hydoferripyrophyllit.

The mineral was first described in 1827 by Pierre Berthier scientifically. His type handpiece Mineralogy Museum is located in the École Nationale Supérieure des Mines in Paris.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the nontronite belonged to the mineral class of " silicates and Germanates " and then to the Department of " layer silicate minerals ( phyllosilicates ) ," where he, along with beidellite, Brinrobertsit, montmorillonite, Swinefordite volkonskoite and Yakhontovit the unnamed group VIII/H.19 formed.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the nontronite in the class of " silicates and Germanates " and there in the department of " layer silicate minerals ( phyllosilicates ) ". This division, however, is further subdivided according to the type of film formation, so that the mineral according to its construction in the subsection " layer silicates ( phyllosilicates ) with mica sheets, composed of tetrahedral and octahedral nets " can be found, where it together with beidellite, Kurumsakit, montmorillonite, volkonskoite ( Redefines recognized by the CNMNC ) and Yakhontovit the " montmorillonite " with the system no. 9.EC.40 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the nontronite in the class of " silicates and Germanates " and there in the department of " layer silicate minerals " one. Here he is with beidellite, montmorillonite, and volkonskoite Swinefordite in the " smectite ( dioctahedral smectites ) " with the system no. To find " layers of six-membered rings with 2:1 phyllosilicates clay minerals " 71.03.01a within the subdivision of.

Mixed batches and varieties

Nontronite forms with a limited beidellite mixed batch. Beidellite has up to one atom of Fe3 per formula unit, nontronite more than two atoms per formula unit. Montmorillonite and nontronite can also be viewed as a mixed number, the comes about by the substitution of Al3 for Fe3. Also in this case, the mixed batch is not complete, there is a very large compound space between 25 and 75 mol% of Fe 3 .

A variety represents the chromium - nontronite

Education and Locations

Nontronite is a weathering product of biotite, and generally of basalts, kimberlites and other ultramafic rocks (found as Kluftbestege and coatings in these rocks ). He can also displace pseudomorphic hornblende and pyroxene. Occasionally, it is also observed as impregnation in porous rocks of olivine basalts contact.

Nontronite also occurs in poorly drained volcanic ash soils. In some of the mineral deposits he was hydrothermally enriched by silicon and iron solutions ( for example, in graphite and sulphide deposits ); Furthermore, he formed hydrothermally at ocean ridges and other exit points in the deep sea. In kontaktmetamorph altered limestones nontronite may also occur. It is formed in recent marine sediments Authigen. Perhaps also play microorganisms at its birth an important role.

Accompanying minerals of nontronite include Apophyllite, calcite, chabazite, hollandite, pyrite, quartz ( chalcedony and opal with the varieties ), siderite and Strengit.

Nontronite can displace the previously formed laumontite in volcanic gas bubbles.

Locations in France next to the type locality in the Dordogne are the departments of Charente, Haute -Vienne, Rhône and Saône -et -Loire. Deposits in Germany are located in Bavaria Hagendorf, in Hessen Vogelsberg mountains, in Lower Saxony at Goettingen and at St. Andrew Berg and Saxony at Geilsdorf and Wolkenstein. Nontronite It also occurs in the following countries:

• Australia (New South Wales, South Australia )
• Brazil ( Minas Gerais )
• India (Maharashtra)
• Kazakhstan
• Mexico (Chihuahua )
• Madagascar
• Namibia (Tsumeb )
• Norway ( in Froland )
• Poland ( in Strzegom )
• Portugal ( in Sátão )
• Russia ( in Perm )
• Sweden ( in Vittensten )
• Slovakia
• Spain ( in Girona)
• Hungary ( Matra Mountains)
• Venezuela
• United States (Arizona, Colorado, Hawaii, California, North Carolina, New Mexico, Pennsylvania, Utah, Washington and West Virginia)

Deposits on Mars

There is reason to believe that nontronite is present even on the planet Mars. The first indications already provided Mariner 9 in 1971, which were then confirmed in 1975 by the Viking 1 and Viking 2 (The X-ray spectrometer of the two probes were up to 47% nontronite ). These suspicions were confirmed by the infrared spectrometer of Mars Express

Crystal structure

Nontronite crystallizes in the monoclinic crystal system, space group C2 / m ( Raumgruppen-Nr. 12) with the lattice parameters a = 5.28 Å; b = 9.14 Å; c = 9.28 Å and 101.0 ° and β = 2 formula units per unit cell.

The basic building blocks of Nontronitstruktur are:

• [ SiO4 ] 4 - tetrahedra and
• [Fe ( III) O6 ] 9 - octahedron.

The tetrahedra are linked through common oxygen atoms to pseudohexagonal layers. Two of these tetrahedral layers are each held together by a layer of octahedrally coordinated Fe3 cations. The linking of the individual octahedra within the octahedral layer is via common edges. When nontronite are just two of the three central octahedral positions occupied by the Fe3 cations, the mineral is therefore dioctahedral. The layers are stacked in the direction ( along the crystallographic c -axis) and indeed in the sequence TOT ( tetrahedral - octahedral - tetrahedral ). The link between the tetrahedra and octahedra via common corners, the tetrahedra are oriented so each with a tip in the direction of the octahedron. The nontronite counts by the TOT sequence thus the 2-1 - or three-layer clay minerals.

Within the tetrahedral layers, substitution of Si4 ions by means of Fe3 - up to a ratio of 1:8 and / or Al3 cations. In the octahedra can be substituted Fe3 by Al3 and Mg2 . By the substitution results in a negative layer charge, which is concentrated to more than 60% in the tetrahedron layer. The charge compensation is accomplished by the incorporation of cations such as Na , Ca2 and Mg2 Occasionally, located between the TOT layers and also link them with each other. In these intermediate layers also store a water molecules. Nontronite is thus a cation exchanger and swellable by water installation.