Kamacite

• Bar iron

Kamacite, also known as a bar of iron, is a nickel-containing variety of iron meteoritic origin. Until 2006 was kamacite as a separate mineral, it was then but of the International Mineralogical Association (IMA ) discredited and reduced to the status of a Eisenvarietät ..

Kamacite has a nickel content from 4 to 7.5 %, crystallizes in the cubic crystal system with body-centered cubic crystal structure and developed in iron meteorites tabular crystals in black to gray in color, surrounded by brightly colored, flaky nickel-rich taenite. Especially good can be viewed in cross-section sanded meteorite samples where they appear bar-shaped and, together with taenite called Widmanstätten figures, these crystals. Kamacite occurs in mm - large, irregular crystals also in all chondrites.

At a proportion of 20 to 50 % of nickel in the compound is Taenite which has a different crystalline structure. At a Ni content of 50% to Tetrataenite forms. A fine intergrowth of kamacite and taenite is called Plessit.

Etymology and history

The mineral name kamacite (bar iron), taenite ( strip) and Plessit ( filling iron ) were coined by Karl von Reichenbach, 1861. The word derives from the Greek kamacite κάμαζ kamask what " bar ", " floor ", " journal " means and due to the beam- shaped design is that is visible in the polished.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the kamacite belonged to the mineral class of " elements " and then to the Department of " metals and intermetallic alloys ( semimetals ) ", where he, together with iron, manganese and Wairauit " iron - series" with the system number. I/A.07 formed.

The 9th edition used since 2001, valid and of the International Mineralogical Association (IMA ) of the Strunz'schen mineral systematics ordered the kamacite to 2005, also in the department of " metals and intermetallic compounds " and then in the " iron kamacite group " with system no. 1.AE.05 within the subdivision of the " iron-chromium- family '. Since kamacite, however, has lost its mineral status since 2006, he is no longer listed in the current Strunz'schen systematics.

The mostly commonly used in English-speaking classification of minerals according to Dana assigns the kamacite, however, still in the category of " elements " and then in the same department. Here he is with iron, taenite, Tetrataenite, Awaruit, nickel and Wairauit in the " iron-nickel group " with the system no. 01:01:11 within the subdivision " 01:01 elements: metallic elements other than the platinum group " to find.

Education and Locations

Kamacite forms in iron meteorites in the solid state at very slow cooling according to the Fe -Ni phase diagram at temperatures 750-450 ° C from taenite. It is found at the places of impact on the earth iron meteorites. It also forms the decay of cohenite, considered to be stable only at high pressures.

Crystal structure

Kamacite crystallized cubic in space group Im3m ( Raumgruppen-Nr. 229 ) with the lattice parameters a = 2.87 to 2.88 Å and two formula units per unit cell.