Milarite

Milarite
	Milarite crystal specimen from Jaguaraçu, Minas Gerais , Brazil (size: 4 × 3 × 2.9 cm)
General and classification
chemical formula	KCa 2 Be 2 Al [Si 12 O 30 ] · H 2 O
Mineral class; (and possibly department)	Silicates and Germanates
System no. to Strunz ; and to Dana	9.CM.05 ( 8th edition : VIII / E.22) ; 63.02.01a.12
Similar minerals	Osumilith
Crystallographic Data
Crystal system	hexagonal
Crystal class ; symbol	dihexagonal-dipyramidal; 6 / m 2 / m 2 / m
Space group	P 6 / mcc (No. 192)
Lattice parameters	a = 10.41 Å ; c = 13.79 Å
Formula units	Z = 2
Frequent crystal faces	hexagonal prism
Physical Properties
Mohs hardness	6th
Density (g / cm 3 )	2.6
Cleavage	no
Break ; Tenacity	shell-like, brittle
colour	colorless, yellowish, greenish
Line color	White
transparency	transparent to translucent
shine	Glass gloss
Other properties
Special features	Luminescence

Milarite is a rather seldom occurring mineral from the mineral class of " silicates and germanates " with the idealized chemical formula KCa ₂ Be ₂ Al [Si ₁₂ O ₃₀ ] · H ₂ O and is thus a water-containing potassium - calcium - beryllium - aluminum silicate . Structurally, milarite belongs to the ring silicates ( cyclosilicates ).

Milarite crystallizes in the hexagonal crystal system and develops mostly needle-like to long prismatic crystals , but also occurs in the form of granular mineral aggregates . In its pure form, milarite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a gray, light yellow or light green color, the transparency decreasing accordingly.

Etymology and history

The name of the milarite, discovered in the 1870s, is derived from the locality Val Milà in Tujetsch / Canton Graubünden ( Switzerland ), which was originally thought to be the first place where it was found. However, it turned out that the sample examined at the time came from the Val Giuv immediately to the west . Since then, numerous sites have been found around the world. However, it can be assumed that milarite occurs far more frequently than previously assumed, because it can easily be confused with apatite or even with quartz (rock crystal) due to its appearance ( crystal costume , habit , color), its physical properties and the typical paragenesis may often be overlooked.

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the milarite belonged to the general division of " ring silicates (cyclosilicates)", where together with Osumilith it formed the " milarite-osumilith group " with system no. VIII / E.22 and the other members Almarudit , Armenit , Berezanskit , Brannockit , Chayesit , Darapiosit , Dusmatovit , Eifelit , Emeleusit , Faizievit , Merrihueit , Oftedalit , Osumilith- (Mg) , Poudretteit , Roedderit , Shibkovit , Sogdianit , Sugilith , Trattnerit , Yagiit and Yakovenchukit- (Y) made.

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 milarite in the “ring silicates” section. This is, however, further subdivided according to the structure of the rings, so that the mineral, according to its structure, can be found in the subsection "[Si ₆ O ₁₈ ] ¹²⁻ -six-double rings", where the " milarite group " is the sole namesake System no. 9.CM.05 and the other members Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit , Klöchit , Merrihueit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderit, Shibkovit, Sogdianit , Trattnerite and yagiit forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the milarite to the class of "silicates and germanates", but there it is in the more finely divided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.

Crystal structure

Unbranched 6-double ring of milarite

Milarite crystallizes hexagonally in the space group P 6 / mcc (space group no. 192) with the lattice parameters a = 10.41 Å and c = 13.79 Å and 2 formula units per unit cell . Template: room group / 192

Milarite is a ring silicate with unbranched 6-double rings as an anion complex.

Education and Locations

Perfectly grown, dihexagonal-dipyramidal milarite crystal

Radial milarite from Middle Moat Mountain , Carroll County (New Hampshire) , New Hampshire, USA (size: 7.4 cm × 6.9 cm × 3.9 cm)

Milarite is an extremely low pressure mineral and is formed at temperatures of approx. 250 to 200 ° C and in the presence of alkaline fluids . The mineral therefore occurs in late magmatic rocks such as pegmatites and miaroles in plutonites , in hydrothermal ore deposits and as alpine fissure mineral . Milarite is also known as an alteration product of other beryllium minerals.

Classic sites of milarite are in the central Swiss Alps , e.g. B. in the area of the Vorderrhein Valley ( Val Giuv , Val Strem , Val Val ), at the Tysfjord in Norway and in Namibia ( Rössing mine ).

use

The use of milarite is limited to the occasional processing into gemstones . Milarite in gem quality is known from the occurrence of the Rössing mine in Namibia.

Web links

Commons : Milarite - collection of images, videos and audio files

Individual evidence

↑ ^a ^b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th, completely reworked and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
^ ^A ^b ^c Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 613 .
^ IMA / CNMNC List of Mineral Names; November 2015 (PDF 1.6 MB)
↑ G. Strübel, SH Zimmer: Lexicon of Minerals. Enke Verlag, Stuttgart 1991, ISBN 3-432-92722-3 .
↑ ^a ^b ^c FC Hawthorne, M. Kimata, P. Černý, N. Ball, GR Rossman, JD Grice: The crystal chemistry of the milarite-group minerals. In: American Mineralogist. Volume 76, 1991, pp. 1836-1856.
^ HA Stalder, A. Wagner, S. Graeser, P. Stuker: Mineralienlexikon der Schweiz . Wepf, Basel 1998.
↑ T. Husdal: The minerals of the pegmatites within the Tysfjord granite, northern Norway. In: Norsk Bergverksmuseum skrift. Volume 38, 2008, pp. 5-28.
↑ ^a ^b TP Moore: Alpine milarite. In: The Mineralogical Record. Volume 35, 2004, pp. 405-418.
^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 43 (first edition: 1891).

[Lapis-1] Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th, completely reworked and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .

[StrunzNickel-2] A ^b ^c Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 613 .

[IMA-Liste-2015-11-3] IMA / CNMNC List of Mineral Names; November 2015 (PDF 1.6 MB)

[StrübelZimmer-4] G. Strübel, SH Zimmer: Lexicon of Minerals. Enke Verlag, Stuttgart 1991, ISBN 3-432-92722-3 .

[Hawthorne_et_al._1991-5] FC Hawthorne, M. Kimata, P. Černý, N. Ball, GR Rossman, JD Grice: The crystal chemistry of the milarite-group minerals. In: American Mineralogist. Volume 76, 1991, pp. 1836-1856.

[Stalder-et-al-6] HA Stalder, A. Wagner, S. Graeser, P. Stuker: Mineralienlexikon der Schweiz . Wepf, Basel 1998.

[Husdal-7] T. Husdal: The minerals of the pegmatites within the Tysfjord granite, northern Norway. In: Norsk Bergverksmuseum skrift. Volume 38, 2008, pp. 5-28.

[Moore_2004-8] TP Moore: Alpine milarite. In: The Mineralogical Record. Volume 35, 2004, pp. 405-418.

[Klockmann-9] Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 43 (first edition: 1891).