AUTHOR=Atencio Daniel 

TITLE=Pyrochlore-Supergroup Minerals Nomenclature: An Update

JOURNAL=Frontiers in Chemistry

VOLUME=9

YEAR=2021

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2021.713368

DOI=10.3389/fchem.2021.713368

ISSN=2296-2646

ABSTRACT=<p>The general formula of the pyrochlore-supergroup minerals is <italic>A</italic><sub>2</sub><italic>B</italic><sub>2</sub><italic>X</italic><sub>6</sub><italic>Y</italic>. The mineral names are composed of two prefixes and one root name (identical to the name of the group). The first prefix refers to the dominant anion (or cation or H<sub>2</sub>O or vacancy) of the dominant valence at the <italic>Y</italic>-site. The second prefix refers to the dominant cation of the dominant valence [or H<sub>2</sub>O or vacancy] at the <italic>A</italic>-site. Thirty-one pyrochlore-supergroup mineral species are currently distributed into four groups [pyrochlore (<italic>B</italic> = Nb, <italic>X</italic> = O), microlite (<italic>B</italic> = Ta, <italic>X</italic> = O), roméite (<italic>B</italic> = Sb<sup>5+</sup>, <italic>X</italic> = O), and elsmoreite (<italic>B</italic> = W, <italic>X</italic> = O)] and two unassigned members [hydrokenoralstonite (<italic>B</italic> = Al, <italic>X</italic> = F) and fluornatrocoulsellite (<italic>B</italic> = Mg, <italic>X</italic> = F)]. However, when the new nomenclature system of this supergroup was introduced (2010) only seven mineral species, namely, oxycalciopyrochlore, hydropyrochlore, hydroxykenomicrolite, oxystannomicrolite, oxystibiomicrolite, hydroxycalcioroméite, and hydrokenoelsmoreite, were valid. The seven species belong to the cubic crystal system and space group <italic>Fd</italic><inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula><italic>m</italic> and O is predominant in the <italic>X</italic> structural site. The 24 new mineral species described between 2010 and 2021 are cesiokenopyrochlore, fluorcalciopyrochlore, fluornatropyrochlore, hydrokenopyrochlore, hydroxycalciopyrochlore, hydroxynatropyrochlore, hydroxykenopyrochlore, hydroxymanganopyrochlore, hydroxyplumbopyrochlore, fluorcalciomicrolite, fluornatromicrolite, hydrokenomicrolite, hydroxycalciomicrolite, kenoplumbomicrolite, oxynatromicrolite, oxycalciomicrolite, oxybismutomicrolite, fluorcalcioroméite, hydroxyferroroméite, oxycalcioroméite, oxyplumboroméite, fluornatrocoulsellite, hydrokenoralstonite, and hydroxykenoelsmoreite. Among the new species, hydroxycalciomicrolite belongs to a different space group of the cubic system, i.e., <italic>P</italic>4<sub>2</sub>32. There are also some mineral species that crystallize in the trigonal system. Hydrokenoelsmoreite occurs as 3<italic>C</italic> (<italic>Fd</italic><inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula><italic>m</italic>) and 6<italic>R</italic> (<italic>R</italic><inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>) polytypes. Hydrokenomicrolite occurs as 3<italic>C</italic> (<italic>Fd</italic><inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula><italic>m</italic>) and 3<italic>R</italic> (<italic>R</italic><inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula><italic>m</italic>) polytypes, of which the latter corresponds to the discredited “parabariomicrolite.” Fluornatrocoulsellite crystallizes as 3<italic>R</italic> (<italic>R</italic><inline-formula id="inf6"><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mn>3</mml:mn><mml:mo>¯</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula><italic>m</italic>) polytype. Surely there are several new pyrochlore-supergroup minerals to be described.</p>