Nacrite
- Steinmarkskopf
Nacrite outdated, also known as Mark Stone, is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic crystal system with the composition Al4 [( OH) 8 | Si4O10 ], is thus seen chemically crystal layer silicate with an aluminum hydroxide ( (OH) 2 - ) as an additional anion
Nacrite usually develops earthy, scaly or massive aggregates, rarely small, tabular, irregular pseudo-hexagonal crystals of white, gray or yellowish brown in color and pearly luster.
Etymology and history
Was first described in 1807 by Alexandre Brongniart nacrite. Was named the mineral because of its luster after the French word for pearl nacre.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the nacrite belonged to the general ward of the " layer silicates ( phyllosilicates ) ," where he along with dickite, halloysite - 7 Å and kaolinite the " kaolinite - group " with the system No. VIII/H.25 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the nacrite also in the department of " layer silicates ( phyllosilicates ) " a. However, this is further divided according to the structure of the layers, so that the mineral according to its construction in the subdivision " layer silicates ( phyllosilicates ) with kaolinite layers composed of tetrahedral or octahedral networks " is to find where it together with dickite, kaolinite, and Odinit the " kaolinite - group " with the system no. 9.ED.05 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the nacrite in the department of " layer silicate minerals " one. Here he is as together with dickite, kaolinite, halloysite - 7 Å, Endellit and Odinit in the " kaolinite " with the system no. 71.01.01 within the subdivision: to find " layer silicates layers of six-membered rings with 1:1 layers ".
Modifications and varieties
A variety of grobschuppige nacrite is called Pholerit.
Education and Locations
Nacrite forms in cavities of hydrothermal deposits. Accompanying minerals include calcite, dolomite, fluorite, quartz and topaz.
A rare mineral formation nacrite previously could (as of 2012) are detected only at a few localities, of which approximately 100 localities are known. Apart from its type locality pit unity at Brand-Erbisdorf the mineral still occurred in Germany in some other mines in the Saxon Erzgebirge evident. Other localities include Schweighausen in the Black Forest in Baden- Württemberg; Berneck, Joditz and Wölsendorf ( Schwandorf ) in Bavaria, Sankt Andreas mountain in Lower Saxony Harz, the mines Zollverein, Julia and Wilder Mann in North Rhine -Westphalia, Bad Ems and Dannenfels in Rhineland -Palatinate, the pit basket on iron ( Nohfelden ) in Saarland and Ronneburg and in the quarry Henneberg at Weitisberga in Thuringia.
In Austria, nacrite found previously only on the Katschberg, more precisely in rock samples that were taken during the construction of the Katschberg tunnel on the Tauern motorway between Salzburg and Carinthia.
Other localities lie among others in Argentina, Australia, Bolivia, China, France, Italy, Japan, Canada, Kazakhstan, the Democratic Republic of Congo, Mexico, Namibia, Poland, Sweden, Slovakia, Spain, South Africa, South Korea, Czech Republic, Ukraine, Hungary, the United Kingdom (UK) and the United States of America (USA).
Crystal structure
Nacrite crystallizes in the monoclinic crystal system in the space group Cc ( Raumgruppen-Nr. 9) with the lattice parameters a = 8.91 Å, b = 5.15 Å, c = 15.70 Å and β = 113.7 ° and two formula units per unit cell.