Tarbuttite

Tarbuttit is a naturally occurring mineral from the mineral class of " phosphates, arsenates and vanadates ." It crystallizes in the triclinic crystal system with the chemical composition of Zn 2 [ OH | PO4 ], and is therefore a zinc phosphate with additional hydroxide.

Tarbuttit most developed area- rich, isometric to short prismatic or pseudo-cubic crystals up to about two inches in size but also occurs in the form sheaf -like mineral aggregates and crusty coatings. In its pure form Tarbuttit is colorless and transparent. But it may also appear white and accept by foreign admixtures a yellowish, reddish, greenish or brownish color by multiple refraction due to lattice defects or polycrystalline training, the transparency decreases accordingly. Uninjured crystal faces have a glass-like luster, cleavage surfaces shimmer on the other hand rather nacreous.

Etymology and history

Was first discovered in the Tarbuttit " Kabwe Mine" (Broken Hill Mine ) near the eponymous town Kabwe in the Central Province of Zambia and described in 1907 by Leonard James Spencer ( 1870-1959 ), who named the mineral after Percy Coventry Tarbutt. Tabutt at the time was director of the "Broken Hill Exploration Company " and discovered the mineral near a cave with ice-age mammoth bones.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Tarbuttit belonged to the mineral class of " phosphates, arsenates and vanadates " and then to the Department of " water clear phosphates, with foreign anions F, Cl, O, OH ", where he along with Adamite, Eveit, Libethenit, Olivenit, Paradamin, Zincolibethenit and Zinkolivenit the " Libethenit group " with the system no. VII/B.06 formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Tarbuttit also in the department of " phosphates, etc., with additional anions, without H2O" one. However, this is further divided according to the relative size of the involved cations and the molar ratio of the added anions (OH, etc. ) to the phosphate, arsenate or Vanadatkomplex ( RO 4 ), so that the mineral according to its composition in the subsection "With only medium-sized cations, (OH, etc.): RO 4 " is to find where it is named as the " " less than" 1:1 Tarbuttitgruppe "with the system no. 8.BB.35 and the other Member Paradamin forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the Tarbuttit in the class of " phosphates, arsenates and vanadates " and there in the department of " water clear phosphates, etc., with hydroxyl or halogen" one. Here he is with Para order in the " Tarbuttitgruppe " with the system no. 41.06.07 found within the subdivision " Anhydrous Phosphates, etc., with hydroxyl or halogen with (A ) 2 ( XO4 ) Zq ".

Education and Locations

Tarbuttit formed secondarily in the oxidation zone of zinc-containing deposits. Accompanying minerals may include cerussite, Descloizit, hemimorphite Hopeit and Parahopeit, Hydrozincite, pyromorphite, scholzite, Smithsonite, Vanadinit and the limonite limonite.

As a very rare mineral formation Tarbuttit previously could (as of 2013 ) can be detected from fewer than 10 archaeological sites in only a few samples. Its type locality " Kabwe Mine " is the only known locality in Zambia.

Other previously known localities are Broken Hill and Reaphook Hill ( Flinders Ranges ) in Australia, Albères in the French department of Pyrénées- Orientales, the " Scorpion Mine" in Rosh Pinah in Namibia and Iowa Gulch near Leadville in the U.S. state of Colorado.

Crystal structure

Tarbuttit crystallizes in the triclinic space group P1 ( Raumgruppen-Nr. 2) with the lattice parameters a = 5.50 Å; b = 5.65 Å; c = 6.46 Å; α = 102.9 °; β = 102.8 ° and γ = 86.8 ° and two formula units per unit cell.

The crystal structure consists of chains of edge-sharing components of ZnO3 (OH ) 2, form the trigonal Dipyramiden parallel and two dimers of edge-sharing ZnO3 (OH ) trigonal Dipyramiden. Both modules and RO4 tetrahedra are connected with one another via the edges and form a 3-dimensional structure.

762066
de