Povondraite is a rare

silicate mineral Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

from the

tourmaline Tourmaline ( ) is a crystalline silicate mineral, silicate mineral group in which boron is chemical compound, compounded with chemical element, elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a ...

group with formula: NaFe³⁺₃(Fe³⁺₄,Mg₂)(BO₃)₃Si₆O₁₈(OH)₃O."Povondraite"
on

Mindat.org Mindat.org is a non-commercial interactive online database covering minerals around the world. Originally created by Jolyon Ralph as a private project in 1993, it was launched as a community-editable website in October 2000. it is operated by ...

It is a dark brown to black nearly opaque mineral with a resinous to splendent luster. It crystallizes in the

trigonal crystal system In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

as equant, distorted prisms with trigonal pyramid terminations.Handbook of Mineralogy
/ref> It occurs as rare fracture and cavity encrustations within

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

s derived from sedimentary rocks. Associated minerals include

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

potassium feldspar Potassium feldspar refers to a number of minerals in the feldspar group that contain large amounts of potassium in the crystal lattice. *Orthoclase (endmember formula K Al Si3 O8), an important tectosilicate mineral that forms igneous rock *Microcl ...

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...

schorl Tourmaline ( ) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors. The name is derived from th ...

riebeckite Riebeckite is a sodium-rich member of the amphibole group of silicate minerals, chemical formula Na2(Fe2+3Fe3+2)Si8O22(OH)2. It forms a solid solution series with magnesioriebeckite. It crystallizes in the monoclinic system, usually as long ...

and

magnesite Magnesite is a mineral with the chemical formula ( magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts. Occurrence Magnesite occurs as veins in and an alteration product of ultramafic r ...

. Discovered at the San Francisco mine, near

Villa Tunari Villa Tunari or Tunari is a location in the department of Cochabamba Department, Cochabamba, Bolivia. It is the seat of the Villa Tunari Municipality, the third Municipalities of Bolivia, municipal section of the Chapare Province. According to t ...

(in Alto Chapare),

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

, in 1976, originally it was called ferridravite, for the composition and the assumed relationship to

dravite Tourmaline ( ) is a crystalline silicate mineral group in which boron is compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. This gemstone comes in a wide variety of colors. The name is derived from th ...

, i.e., "ferric dravite". However later investigations yielded a new empirical formula which had no relation to the dravite. This called for renaming, and the new name, after Pavel Povondra (1924–2013), a mineralogist at the

Charles University in Prague Charles University (CUNI; , UK; ; ), or historically as the University of Prague (), is the largest university in the Czech Republic. It is one of the oldest universities in the world in continuous operation, the oldest university north of the ...

, was approved by the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. ...

in the 1990s.Joel, D. Grice, T. Scott Encit, Frank C. Hawthorn
"Povondraite. a redefinition of the tourmaline ferridravite"
American Mineralogist, Volume 78, pages 433-436, 1993

References

{{reflist Cyclosilicates Iron(III) minerals Manganese minerals Sodium minerals Trigonal minerals Minerals in space group 160 Tourmalines