Sérandite
Serandit is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the triclinic crystal system with the idealized chemical composition NaMn2 2 Si3O8 (OH ), is therefore a chemical point of a sodium manganese silicate.
Structurally Serandit to the chains and band silicates with additional hydroxide ions. In addition, it forms with Pectolite ( NaCa2Si3O8 (OH )) is a solid solution series. Accordingly, the manganese contained in the formula is often replaced by small amounts of calcium in natural Serandit. Both can be developed by using the Strunz crystal chemical structural formula in the form of Na (Mn 2 , Ca) express 2 [ Si3O8 (OH)].
In its pure form Serandit is colorless and transparent. But it may also appear white and accept by foreign admixtures a light pink to pink, red, brown or black color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. However, his stroke color is always white.
Serandit most developed prismatic to acicular and platy or blocky crystals, but also occurs in the form radialstrahliger and massive mineral aggregates. Uninjured or unweathered crystal faces have a glass - to -fat -like gloss on the other hand, cleavage surfaces show pearly and massive aggregates are dull.
With a Mohs hardness from 5 to 5.5 Serandit belongs to the medium-hard minerals that are similar to how the reference minerals apatite (5) and orthoclase (6 ) with a pocket knife or a steel file can scratch.
Etymology and history
Serandit was first discovered on the belonging to the Îles de Los island Roume in Guinea and described in 1931 by Antoine Lacroix, who named the mineral after his assistant JM Sérand.
Type material of the mineral is in the National Museum of Natural History in Washington, DC kept ( Register-Nr. 96515 ).
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Serandit belonged to the department of " chains and chain silicates ( inosilicates ) " where he along with Bustamite, Cascandit, Denisovite, Ferrobustamit, Foshagite, Jennit, Pectolite, Tanohatait, Vistepit and wollastonite, the " Wollastonitgruppe " with the system number. VIII/F.18 formed.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Serandit also in the department of " chains and chain silicates " one. However, this is further subdivided according to the type of chain formation, so that the mineral is " with 3- periodic single and multiple chains chains and chain silicates " to find according to its construction in the subdivision where it together with Bustamite, Ferrobustamit, Pectolite, Tanohatait and wollastonite, the " Wollastonitgruppe " with the system number. 9.DG.05 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the Serandit in the department of " chain silicate minerals " one. He is also in the " Wollastonitgruppe " with the system no. 65.02.01 within the subdivision " chain silicates: Simple unbranched chains, W = 1 with chains P = 3" to find.
Education and Locations
Serandit formed by hydrothermal processes in cavities of volcanic rocks such as nepheline syenites, pegmatites and carbonatites. Accompanying minerals stood beside nepheline on, you still aegirine, analcime, Arfvedsonite, Astrophyllite, eudialyte, Leukophanit, microcline, manganese Neptunite, sodalite and Villiaumit.
A rare mineral formation Serandit could be proven so far only in a few localities, where previously some 30 localities (as of 2013) are considered to be known and its type locality Roume is the only known locality in Guinea.
The most massive and at the same time best crystals with up to 20 centimeters in length have been found at Mont Saint- Hilaire in Canada. Mont Saint- Hilaire is also known for its pseudomorphs of Rhodochrosite after Serandit. Up to 6 inches long Séranditkristalle appeared in " Yubileinaya " Pegmatitgang on the mountain Karnassurt Lovozero massif ( Lovozero Tundra ) on the Russian Kola Peninsula to light.
Other localities lie including Australia, Brazil, Italy, Japan, Namibia, Norway, South Africa and the United States of America (USA).
Crystal structure
Serandit crystallizes in the triclinic space group P1 ( Raumgruppen-Nr. 2) with the lattice parameters a = 7.68 Å; b = 6.89 Å; c = 6.75 Å; α = 90.5 °; β = 94.1 ° and γ = 102.7 ° and two formula units per unit cell.