Neptunite
The mineral Neptunite is a rarely occurring chain silicate from the Neptunite group. It crystallizes in the monoclinic crystal system with the idealized chemical composition KNa2Li ( Fe2 ) 2Ti2Si8O24 and thus belongs in chemical terms to the complex composition layer silicates with transition structures to other silicates and metal cations potassium, sodium, lithium, iron and titanium.
Neptunite usually develops long-prismatic, sometimes bent or twisted crystals to about eight centimeters in length, usually with square cross-sections. The predominantly opaque and dark brown to black crystals exhibit on their surfaces a glass-like shine. In thin films, however Neptunite blood red translucent and on the dash board, it leaves a red-brown to zimtbraunen line.
With a Mohs hardness 5-6 Neptunite belongs to the medium-hard minerals that can be good to just scratched with a knife or similar to the reference minerals fluorite ( 5) and apatite (6).
Chemistry
In nature Neptunite usually occurs at levels of manganese, which are always placed as iron and manganese in the formula each represent each other ( Diadochie ), in the same proportion to the other constituents of the mineral. The chemical composition is according to different sources KNa2Li ( Fe2 , Mn) 2Ti2 [ O2 | Si8O22 ] specified.
With increasing content of manganese Neptunite finally goes over (even Manganoneptunit, KNa2Li ( Mn2 ) 2Ti2Si8O24 ) in the mineral manganese Neptunite. Neptunite and manganese Neptunite thus form a complete solid solution series.
When also related mineral Watatsumiit that contained in the formula of the Neptunite titanium is replaced by vanadium.
Special Features
Neptunitkristalle show a piezoelectric effect, ie they build similar to the known quartz with varying elastic deformation of an electrical voltage.
Etymology and history
Was first discovered Neptunite in a pegmatite at Narsaarsuk ( Narssârssuk ) in West Greenland and described in 1893 by Gust Flink, who named the mineral after the god Neptune in Roman mythology.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Neptunite belonged to the mineral class of " silicates and Germanates " and then to the Department of " chain silicates and phyllosilicates ( inosilicates ) ", where he held a along with manganese Neptunite and Watatsumiit independent group was formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Neptunite also in the class of " silicates and Germanates " there, however, in the department of " layer silicates ( phyllosilicates ) " a. This department is also further subdivided by the structural composition of the layers, so that the mineral is found in accordance with its construction in the subsection "transitional structures between phyllosilicates and other silicates ", where it also together with manganese Neptunite and Watatsumiit named after him " Neptunitgruppe "with the system number. 9.EH.05 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the Neptunite in the class of " silicates and Germanates " there, however, in the department of " chain silicates: Column or Tube Structures" one. Here it is again as a name in the " Neptunitgruppe " with the system no. 70.04.01 and the other members manganese Neptunite, Watatsumiit and Magnesioneptunit within the subdivision: to find " chain silicates columns or tubular structures with associated chains in cage form ".
Education and Locations
Neptunite forms in natrolite veins that cut trapped in Serpentinitkörpern layers of glaucophane - schist. Accompanying minerals are next Natrolite, you still aegirine, Arfvedsonite, Benitoite, eudialyte, Joaquinite - (Ce), Lomonosovit, nordIT - ( La), sodalite and ussingite.
A rare mineral formation Neptunite previously could (as of 2011) are detected only at a few localities, with about 40 localities are known. Apart from its type locality Narsaarsuk the mineral still occurred at several places in the Ilímaussaq intrusion around Narsaq in County Kitaa in Greenland.
Noteworthy for its exceptional Neptunitfunde is especially the " Dallas Gem Mine " at the San Benito River in the same county in the U.S. state of California, where beautifully developed and up to eight inches long crystals were found.
Other localities lie among others in Australia ( New South Wales ), Brazil ( Minas Gerais, Santa Catarina ), Ireland ( County Louth ), Canada ( Newfoundland and Labrador, Quebec ), Mongolia ( Gobi Desert ), Russia ( Siberia, North-West Russia ), Tajikistan ( Tian Shan) and other states in the USA (Montana, New Mexico, North Carolina).
Crystal structure
Neptunite crystallizes in the monoclinic space group Cc ( Raumgruppen-Nr. 9) with the lattice parameters a = 16.48 Å; b = 12.49 Å; c = 10.00 Å and β = 115.4 °, and four formula units per unit cell.