Brucite
Brucite is a rarely occurring mineral from the class of " oxides and hydroxides ". It crystallizes in the trigonal crystal system with the composition Mg ( OH) 2, is so chemically seen a magnesium hydroxide.
Brucite usually develops needle-like crystals of tabular or up to 19 cm in size, but is also found in the form of lush, rosette-shaped, granular, fibrous or massive mineral aggregates of up to 50 cm in size. Uninjured crystal faces have a glass-like luster, cleavage surfaces shimmer contrast nacreous.
In its pure form brucite is colorless and transparent. In multicrystalline training, he can also appear white and accept by lattice defects or foreign admixtures a gray, yellow, brown, greenish or bluish color due to multiple refraction, however, the transparency decreases accordingly. However, the line color is always white.
Special Features
Brucite is pyroelectric, ie built at intervals like heating and cooling an electrical voltage in the crystal.
Before the blowpipe brucite is indeed hazy, but does not melt. He is, however, very sensitive to acid and dissolves in dilute acids already easily.
Etymology and history
Brucite was first discovered in 1824 named in Castle Point in Hoboken in the U.S. state of New Jersey and described by François Sulpice Beudant, of 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In the now outdated but still in use 8th edition of the mineral classification by Strunz the brucite still belongs to the general ward of the " Hydroxide and oxide hydrates " ( crystal hydrous oxides ), where he, along with Amakinit, Ashoverit, para- Otwayit, portlandite, Pyrochroit forms Spertiniit, Sweetit, Theophrastit and Wülfingit an independent group.
The 9th edition valid since 2001 and also by the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification leads the brucite under the Department " Hydroxide (without V or U) " and then in the sub-division of " hydroxides with OH, without H2O; with layers of edge-sharing octahedra, "where he is the unnamed group 4.FE.05 together with Amakinit, Fougèrit, portlandite, Pyrochroit and Theophrastit.
The commonly used in English-speaking classification of minerals according to Dana assigns the brucite in the department of " hydroxides and hydroxy- oxides " and then in the sub-division of " hydroxides and hydroxy- oxides with the formula X2 ( OH) 2 ." Here is the mineral name to the " Brucitgruppe ( rhombohedral: P 3 m 1 < / math > ) " with the system no. 06:02:01 and the other members Amakinit, Pyrochroit, portlandite and Theophrastit.
Modifications and varieties
In brucite Mg 2 can be to a limited extent replaced by Fe2 and Mn2 ( substitution ), the iron-containing brucite is also called Ferrobrucit and manganese as Manganbrucit. However Nemalith is a morphological variety of brucite, wherein the crystals have a fibrous habit.
When Ferrobrucit can be replaced by Fe2 up to 36% Mg2 what makes this variety, however, 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 an opaque dark brown. This is due to the atmospheric oxygen, which ensures oxidation of iron from Fe2 to Fe3 . In addition, this conversion causes a disturbance of the crystal lattice until its complete dissolution. Ferrobrucit is amorphous, i.e., despite retaining the external crystal form is no internal order between the crystal blocks is also using the X-ray structure analysis to determine more.
Education and Locations
In nature, brucite is formed almost exclusively during metamorphosis. It arises from the conversion of magnesium -rich minerals such as dolomite, forsterite and periclase. Brucite is a characteristic mineral of serpentinite and there is formation temperatures of < 400 ° C to. Furthermore you can find in brucite marbles or as a gap mineral. Artificial brucite may arise as a component of the scale.
Worldwide, brucite far (as of 2010) are detected at around 290 localities, including, inter alia in Antarctica, Australia, Brazil, China, Germany, Finland, France, Ghana, Greece, Indonesia, Israel, Italy, Japan, the Jordan, Canada, Libya, Morocco, Mexico, Namibia, New Zealand, North Korea, Norway, Austria, Pakistan, Poland, Romania, Russia, Sweden, Switzerland, Zimbabwe, Slovakia, Spain, South Africa, Czech Republic, Tuvalu, Turkey, the United Kingdom ( UK) and the United States of America (USA).
Crystal structure
Brucite trigonal crystallized in the space group P3m1 with the lattice parameters a = 3.15 Å and c = 4.77 Å, and one formula unit per unit cell.
The structure of brucite consists of two arranged on type of hexagonal close-packed OH layers. In the spaces between the OH layers are octahedrally coordinated Mg cations. These layers consist in two spatial directions ( crystallographic a- and b- axis) continue indefinitely. In the direction of the c axis adjacent layers are held together only by relatively weak van der Waals bonding, this constitutes the perfect cleavage of the mineral. This so-called Brucitschicht ( OH layers with a central cation position ) is a fundamental part of the structure of the layer silicates.
Use
Brucite is a raw material for the production of refractory materials. In the chemical industry artificially produced mainly magnesium hydroxide is employed.