Scandian actinolite from Jordanów Śląski, Lower Silesia, Poland: Compositional evolution, crystal structure, and genetic implications

Abstract

Scandian actinolite evolving to scandio-winchite (up to 5.45 wt% Sc 2 O 3 ) has been found in chlorite-dominant xenoliths incorporated into marginal portion of a granitic pegmatite. The pegmatite intruded a blackwall schist zone developed around rodingite-type rocks exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, ~30 km south of Wrocław, Lower Silesia, Poland. The amphiboles form irregular overgrowths around cascandite and represent a complex solid-solution series among actinolite and scandio-winchite end-members, with a trace contribution of 'scandio-magnesio-hornblende'. Structural studies of a scandian actinolite crystal with composition A ( 0.995(2) K 0.005(2) ) Σ1 B (Na 0.24(5) Ca 1.73(4) ) Σ1.98(1) C (Mg 3.74(7) Fe 2+ 0.90(3) Mn 0.04(1) Sc 0.26(3) Al 0.05(1) ) Σ4.99(1) T (Si 7.98(2) Al 0.02(2) ) Σ8.00 O 22 (OH) 2 revealed monoclinic C2/m structure with unit-cell parameters a = 9.8517(3), b = 18.0881(6), c = 5.28501(18) Å, β = 104.809(4)°, in which scandium is located solely at the C M2 site. Scandian amphiboles are uncommon in geological environments, and invite comments on the origin of the observed Sc enrichment in the amphibole structure. Textural appearance of the chlorite-cascandite-amphibole clusters suggests that the formation of the amphiboles is related to the evolution of the country rocks followed by partial alteration of blackwall schist xenoliths by pegmatite-forming melt.

Heflikite, ideally Ca2(Al2Sc)(Si2O7)(SiO4)O(OH), the first scandium epidote-supergroup mineral from Jordanów Śląski, Lower Silesia, Poland and from Heftetjern, Tørdal, Norway

“…The pegmatite consists mainly of quartz, sodic plagioclase and K-feldspar, with accessory pale green beryl, dark green dravite, and randomly scattered aggregates of greenish yellow clinochlore. Detailed investigations also revealed the presence of biotite, muscovite, spessartine, titanite, zircon, cassiterite, columbite-( Mn pyrochlore-and microlite-group minerals, phenakite, bavenite, bertrandite, milarite, tremolite, diopside, uraninite, aikinite, galena, Sc-rich ixiolite and a few Sc-bearing silicates, including cascandite, Sc-rich actinolite (Pieczka et al, 2024a), scandio-winchite (Pieczka et al, 2024b), kristiansenite, bazzite and heflikite (Pieczka et al, 2023).…”

“…In the Heftetjern pegmatite, it is a part of a diverse assemblage of latestage hydrothermal Sc minerals, including bazzite, cascandite, heftetjernite, kristiansenite, oftedalite, scandiobabingtonite and thortveitite (Raade et al, 2002;Kristiansen, 2009;Chukanov et al, 2017;Steffenssen et al, 2020). The granitic pegmatite at Jordanów Śląski also hosts Sc-rich minerals, such as Sc-rich ixiolite, cascandite, kristiansenite, bazzite, Sc-rich actinolite (Pieczka et al, 2024a), and scandio-winchite (Pieczka et al, 2024b). They formed from metasomatic fluids that infiltrated a contact between the granitic pegmatite and the surrounding rodingite-type calc-silicate rocks and serpentinites, introducing Sc into the pegmatite.…”