Walstromite, BaCa2(Si3O9), from Rankinite Paralava within Gehlenite Hornfels of the Hatrurim Basin, Negev Desert, Israel

Abstract

Walstromite, BaCa2Si3O9, known only from metamorphic rocks of North America, was found in small veins of unusual rankinite paralava within gehlenite hornfelses of the Hatrurim Complex, Israel. It was detected at two localities—Gurim Anticline and Zuk Tamrur, Hatrurim Basin, Negev Desert. The structure of Israeli walstromite [with P 1 ¯ space group and cell parameters a = 6.74874(10) Å, b = 9.62922(11) Å, c = 6.69994(12) Å, α = 69.6585(13)°, β = 102.3446(14)°, γ = 96.8782(11)°, Z = 2, V = 398.314(11) Å3] is analogous to the structure of walstromite from type locality—Rush Creek, eastern Fresno County, California, USA. The Raman spectra of all tree minerals exhibit bands related to stretching symmetric vibrations of Si-O-Si at 650–660 cm−1 and Si-O at 960–990 cm−1 in three-membered rings (Si3O9)6−. This new genetic pyrometamorphic type of walstromite forms out of the differentiated melt portions enriched in Ba, V, S, P, U, K, Na, Ti and F, a residuum after crystallization of rock-forming minerals of the paralava (rankinite, gehlenite-åkermanite-alumoåkermanite, schorlomite-andradite series and wollastonite). Walstromite associates with other Ba-minerals, also products of the residual melt crystallization as zadovite, BaCa6[(SiO4)(PO4)](PO4)2F and gurimite, Ba3(VO4)2. The genesis of unusual barium mineralization in rankinite paralava is discussed. Walstromite is isostructural with minerals—margarosanite, BaCa2Si3O9 and breyite, CaCa2(Si3O9), discovered in 2018.

Instalment of the margarosanite group, and data on walstromite–margarosanite solid solutions from the Jakobsberg Mn–Fe deposit, Värmland, Sweden

“…Walstromite, BaCa 2 Si 3 O 9 , was first described by Alfors et al (1965) from the Big Creek–Rush Creek area, Fresno County, California, USA. It was later reported from several other deposits in Western North America (Dunning et al , 2018) and also from pyrometamorphic rocks (paralavas) of the Hatrurim Formation, Israel (Krzątała et al , 2020). Dent Glasser and Glasser (1968) determined the crystal structure of synthetic walstromite, confirmed subsequently by Barkley et al (2011) using material from the type locality.…”

“…The isostructurality of margarosanite and walstromite was first postulated by Glasser and Glasser (1964) and subsequently confirmed by several authors (Dent Glasser and Glasser, 1968; Freed and Peacor, 1969; Callegari and Boiocchi, 2016; Krzątała et al , 2020).…”

“…Walstromite from Fresno, California shows up to 0.4 wt.% SrO, 0.5% wt.% MnO (RRUFF no. R070634.2, Lafuente et al , 2015) and 0.3 wt.% Al 2 O 3 (Basciano, 1999), whereas walstromite from Hatrurim contains up to 0.4 wt.% TiO 2 and 0.7 wt.% SrO (Krzątała et al , 2020). Furthermore, there is no evidence for substitution between Ca 2+ and the two larger cations Ba 2+ and Pb 2+ in walstromite or margarosanite, respectively.…”

“…Margarosanite clearly has priority in terms of historical precedence, but the structure type has become more familiar under a different name (walstromite). However, neither the ‘margarosanite group’ nor the ‘walstromite group’ seem to have been used as a term used in the past (except for the unapproved use by Krzątała et al , 2020). According to Mills et al (2009), a group name can be selected contrary to the precedence rule when the name of this group is very firmly established in the literature.…”

Bennesherite, Ba2Fe2+Si2O7: A new melilite group mineral from the Hatrurim Basin, Negev Desert, Israel

“…Bennesherite was discovered in the small veins of coarse-grained andradite-rankinite paralava (Fig. 1) within gehlenite-larnite hornfels found at the Gurim Anticline in the Hatrurim Complex (Mottled zone), Negev Desert, Israel (Krzątała et al 2020). The type locality (N 31°12.5′ E35°15.7′) is situated near Arad city, in the central part of the biggest pyrometamorphic rock area in Israel, named the Hatrurim Basin (Gross 1977;Burg et al 1991Burg et al , 1999Vapnik et al (Bentor et al 1963;Gross, 1977;Novikov et al 2013).…”