Brucite

from Wikipedia, the free encyclopedia
Brucite
Brucite-225086.jpg
Brucite from Wood's Chrome Mine, Pennsylvania, USA
General and classification
chemical formula Mg (OH) 2
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FE.05 ( 8th edition : IV / F.03)
02/06/01/01
Similar minerals Talc , chlorite , mica
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3  2 / m
Space group P 3 m 1 (No. 164)Template: room group / 164
Lattice parameters a  = 3.15  Å ; c  = 4.77 Å
Formula units Z  = 1
Frequent crystal faces {11 2 0}, {10 1 1}, {01 1 3}
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) measured: 2.39; calculated: 2.368
Cleavage completely after (0001)
colour colorless, white, gray, yellow, brown, bluish, greenish
Line color White
transparency transparent to opaque
shine Glass luster, mother-of-pearl luster on split surfaces
Crystal optics
Refractive indices n ω  = 1.560 to 1.590
n ε  = 1.580 to 1.600
Birefringence δ = 0.020
Optical character uniaxial positive

Brucite is a rather seldom occurring mineral from the class of " oxides and hydroxides ". It crystallizes in the trigonal crystal system with the composition Mg (OH) 2 , so from a chemical point of view it is a magnesium hydroxide .

Brucite usually develops needle-like or tabular crystals , but is also found in the form of leafy, rosette-shaped, granular, fibrous or massive mineral aggregates up to 50 cm in size. Unharmed crystal surfaces have a glass-like sheen , whereas cleavage surfaces have a mother-of-pearl shimmer.

In its pure form, brucite is colorless and transparent. In the case of multicrystalline formation, however, it can also appear white due to multiple light refraction and can take on a gray, yellow, brown, greenish or bluish color due to lattice construction errors or foreign admixtures, with the transparency decreasing accordingly. However, the line color is always white.

Etymology and history

Brucite was first discovered in 1824 in Castle Point near Hoboken in the US state of New Jersey and described by François Sulpice Beudant , who named the mineral after the American mineralogist Archibald Bruce (1777-1818).

classification

In the now outdated, but still in use, 8th edition of the mineral classification according to Strunz , brucite still belongs to the general division of "hydroxides and oxidic hydrates" ( oxides containing water of crystallization ), where it is found together with amakinite , ashoverite , para-otwayite , portlandite , pyrochroit , Spertiniit , Sweetit , Theophrastit and Wülfingit form an independent group.

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is also used by the International Mineralogical Association (IMA), lists brucite under the section "Hydroxides (without V or U )" and there in the sub-section of "Hydroxides with OH, without H 2 O; with layers of edge-linked octahedra ”, where it forms the unnamed group 4.FE.05 together with amakinite, fougèrite , portlandite, pyrochroite and theophrastite .

The systematics of minerals according to Dana , which is common in the English-speaking world , assigns brucite to the division of "hydroxides and hydroxy- containing oxides" and there in the sub-division of " hydroxides and hydroxy-containing oxides with the formula X 2+ (OH) 2 ". Here the mineral is named after the "brucite group (rhombohedral: P 3 m 1)" with the system no. 02/06/01 and the other members amakinite, pyrochroit, portlandite and theophrastite.

Crystal structure

Brucite crystallizes trigonally in the space group P 3 m 1 (space group no. 164) with the lattice parameters a  = 3.15  Å and c  = 4.77 Å and one formula unit per unit cell . Template: room group / 164

The structure of brucite consists of two OH layers arranged in the manner of the hexagonal closest packing of spheres . The octahedrally coordinated Mg cations are located in the spaces between the OH layers . These layers continue indefinitely in two spatial directions ( crystallographic a and b axes). In the direction of the c-axis, neighboring layers are only held together by a relatively weak van der Waals bond , which is also the reason for the mineral's perfect cleavability.

This so-called brucite layer (OH layers with a central cation layer) is a fundamental component of the structure of sheet silicates .

properties

Contrary to other sources, brucite is not able to show pyroelectric or piezoelectric effects due to its centrosymmetrical crystal structure . Pyro- and piezoelectric effects are described by a polar vector, but crystals with an inversion center are non-polar (see also Neumann's principle ).

In front of the soldering tube , brucite becomes cloudy, but does not melt. However, it is very sensitive to acids and dissolves easily even in dilute acids .

Modifications and varieties

In brucite, Mg 2+ can be replaced to a limited extent by Fe 2+ and Mn 2+ ( substitution ), with iron-containing brucite also being referred to as ferrobrucite and those containing manganese as manganese brucite . Nemalith , on the other hand, is a morphological variety of brucite in which the crystals have a fibrous habit .

In ferrobrucite , up to 36% Mg 2+ can be replaced by Fe 2+ , which makes this variety very unstable. The fresh from the mine brought to light Ferrobrucit is initially colorless and transparent, but then changes within a few days its color from golden yellow to brown to a dark brown opaque. The reason for this is the atmospheric oxygen, which causes the iron to oxidize from Fe 2+ to Fe 3+ . In addition, this transformation causes a disruption of the crystal lattice until it is completely dissolved. Ferrobrucite becomes amorphous , i.e. H. Despite the retention of the external crystal shape, no internal order between the crystal building blocks can be determined even with the help of X-ray structure analysis.

Education and Locations

flaky, bluish brucite from the "Wessels Mine", North Cape, South Africa
Thick-tabular, almost transparent brucite crystal from Wood's Chrome Mine, Texas, Pennsylvania (size 19.5 cm × 14.5 cm × 3.2 cm)
Brucite crystal specimen from "Bazhenovskoe", asbestos, Swerdöpwsl, Russia (size 10.5 cm × 7.8 cm × 7.4 cm)

In nature, brucite is formed almost exclusively during metamorphosis . It arises from the transformation of magnesium-rich minerals such as dolomite , forsterite and periclase . Brucite is a characteristic mineral for serpentinite and shows formation temperatures of <400 ° C. Brucite is also found in marbles or as a fissure mineral . Artificial brucite can be created as a component of the scale .

As a rather rare mineral formation, brucite can be partly abundant in different places, but overall it is not very common. Around 460 sites are known to date (as of 2017).

The “Wood's Chrome Mine” near Texas in Lancaster County (Pennsylvania) , where crystals of up to 19 cm in size were discovered (see picture opposite) as well as the “Low's Mine” (also Pennsylvania) and the “ Tilly Foster Iron Mine ”near Brewster in Putnam County (New York) , which produced crystals up to 18 cm in size. Crystals up to 10 cm in size are known from the “Bazhenovskoe” deposit near asbestos in the Russian Oblast of Sverdlovsk (see picture opposite). A bluish crystal specimen from the same site on display in the terra mineralia in Freiberg is said to have a size of 20 cm × 14 cm × 4 cm.

In Germany, the mineral has so far been found in the Zeilberg quarry near Maroldsweisach in Bavaria, in a gabbro quarry in the Radau valley near Bad Harzburg (see also Harzburger Gabbro ) in Lower Saxony, on a slag dump in the Genna zinc smelter near Letmathe in North Rhine-Westphalia, at several locations in the Eifel ( Arensberg , Bellerberg volcano , Friedrichssegen pit , Hangelberg) and on the Lichtenberg waste dump near Ronneburg in Thuringia.

In Austria, brucite was found in a marble quarry near Kochholz in the community of Dunkelsteinerwald and near Loja in the community of Persenbeug-Gottsdorf in Lower Austria; in a basalt quarry near Klöch , in a serpentinite outcrop at Eibegggraben near Sankt Jakob-Breitenau , in a hard stone quarry near Sankt Lorenzen near Knittelfeld and in several places in the south of the Leoben district in Styria and at Furtschaglkar in the Schlegeisgrund of the Zillertal in North Tyrol.

In Switzerland, the mineral has only been discovered in Val Forno, a side valley of Bergell in the canton of Graubünden, and in the Rimpfischwäng on the Findel glacier near Zermatt in the canton of Valais .

Other locations include the Antarctic, Ethiopia, Australia, Brazil, Chile, China, the Dominican Republic, Finland, France, Ghana, Greece, Indonesia, Ireland, Israel, Italy, Japan, Jordan, Canada, Libya, Morocco, Mexico, Namibia, Nepal, New Zealand, North Korea, Norway, Oman, Pakistan, Poland, Romania, Sweden, Zimbabwe, Slovakia, Spain, South Africa, Taiwan, Czech Republic, Tuvalu, Turkey, Ukraine, Hungary, United Kingdom (UK) and the United States of America (USA).

Brucite could also be detected in soil samples from the prospecting borehole "DSDP hole 778" from the Mariana Trench in the Pacific Ocean.

use

Brucite is a raw material for the manufacture of refractory materials. In the chemical industry, man-made magnesium hydroxide is mainly used.

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d 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.  237 .
  2. ↑ Webmineral - Brucite (English)
  3. ^ A b c d Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  483-484 .
  4. ↑ a b c d Brucite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 70  kB ; accessed on February 26, 2017]).
  5. ↑ a b c d Mindat - Brucite
  6. ↑ a b c d Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  550 (first edition: 1891).
  7. ↑ Walter Borchardt-Ott: Crystallography . 6th edition. Springer-Verlag, Berlin 2002, ISBN 3-540-43964-1 , pp. 158-160, 164 .
  8. ↑ a b A. G. Betechtin (А. Г. Бетехтин): Textbook of special mineralogy . 2nd Edition. VEB Verlag Technik, Berlin 1957, p.  48 (Russian: Курс минералогии . Translated by Wolfgang Oestreich).
  9. ↑ Mindat - Number of localities for Brucite
  10. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 109 .
  11. ↑ Mindat - picture of a 20 cm large brucite crystal specimen from Bazhenovskoe, Asbest, Sverdlovsk, Russia. Exhibited in the terra mineralia
  12. ↑ a b List of places where brucite was found in the Mineralienatlas and Mindat