Controls on Barite Crystal Morphology during Abiotic Precipitation

Abstract

Barite (BaSO4) is a stable and widely distributed mineral in Earth’s crust. As such, barite has the potential to preserve specific geochemical and morphological characteristics representative of conditions at the time of its formation, which could be useful for interpretations of Earth’s ancient rocks and paleoenvironments. In this study, we used variations in saturation index, solution temperature, solution chemistry, presence of organics, and Mg2+ and Ca2+ ions to investigate variations in barite crystal morphology. Through 42 experiments, we simulated poorly understood, low temperature spring settings similar to Zodletone Spring in Anadarko Basin, Oklahoma. Using SEM/EDS, we identified barite rosettes, rounded barite, euhedral/square-shaped barite, and elliptical barite as the crystal morphologies that directly reflect different formational settings. The X-ray diffraction (XRD) patterns revealed different crystallographic characters of the four distinct barite crystal morphologies; in particular, the samples that precipitated from supersaturated SrSO4 solution exhibited double peaks at 43° 2-Theta, which matched barite with strontium substitution as barite might have incorporated strontium in its structure. Barite crystals that formed in the presence of organics in the initial solution exhibited a double peak at 33° 2-Theta, which was absent in other samples. Confocal Raman microscopy indicated that all of the samples had typical barium sulfate bands, with a few differences in bands between the samples; for example, the 638 cm−1 band showed splitting or a double band between different samples. The samples that precipitated from solution with organics had organic compounds from the experimental solution included in their composition. In both cases, C–H stretches from 2800 cm−1 to 3000 cm−1 were present as well as bands from 1350 cm−1 to 1500 cm−1, which are typical of organic compounds. Based on our experiments, the variation in barite crystal morphologies reflected changes in initial solution chemistry (or environmental settings).

Formation of micro‐spherulitic barite in association with organic matter within sulfidized stromatolites of the 3.48 billion‐year‐old Dresser Formation, Pilbara Craton

“…The texture and chemistry of this organic matter‐rich, texturally distinctive nano‐porous pyrite is consistent with an origin through sulfidization of biofilms as early as during stromatolite growth (c.f., Baumgartner, Van Kranendonk, et al, 2020; Baumgartner et al, 2019), as is supported by the presence of entombed, autochthonous organic matter strands and filaments that closely resemble variably degraded and remineralized EPS (compare the organic matter that is encrusted by barite micro‐spherulites in Figure 3f with organic matter strands in Baumgartner et al[2019, their Figure 4]). Hence, while all the physical and chemical factors that can control barite morphology are still not entirely understood (c.f., Widanagamage et al, 2018), our data suggest that intimately associated organics have been important factors for micro‐spherulite formation. These organics were likely derived from (decaying) ancient microbial mats that flourished in a hydrothermally influenced, low‐temperature, shallow water depositional environment (Djokic et al, 2017; Nijman et al, 1998; Van Kranendonk, 2006; Van Kranendonk et al, 2018; Van Kranendonk et al, 2008; Van Kranendonk & Pirajno, 2004; among others).…”

“…On the other hand, barite in the water column and within pelagic sediment typically occurs as rounded, elliptical, or platy tabular grains (e.g., Bertram & James, 1997; Dehairs, Stroobants, & Goeyens, 1991; Griffith & Paytan, 2012). Although the detailed factors in the development of a specific barite morphotype are not entirely understood, laboratory experiments show that variations can be controlled by physical factors such as saturation index, crystal growth rate, and temperature, as well as chemistry, especially the ratio of Ba 2+ /SO4 2− in solution, the presence/abundance of organic molecules, and the availability of ions that may substitute for Ba 2+ in the crystal lattice (Mg 2+ , Ca 2+ , and Sr 2+ ; e.g., Godinho & Stack, 2015; Jones et al, 2007; Judat & Kind, 2004; Kowacz, Putnis, & Putnis, 2007; Ruiz‐Agudo, Putnis, Ruiz‐Agudo, & Putnis, 2015; Smith et al, 2004; Widanagamage, Waldron, & Glamoclija, 2018).…”

“…The incorporation of organic molecules, and perhaps Sr 2+ cations into the crystal lattice of barite, plus organics promoting supersaturation and inhibiting crystal growth, are known to promote the development of both platy tabular/lenticular grains and polycrystalline barite aggregates with spherulitic shape (e.g., Jones et al, 2007; Smith et al, 2004; Widanagamage et al, 2018). The importance of organics in the formation of spherulitic barite is further demonstrated by experiments involving marine microbial cultures, which revealed that cellular surfaces and EPS can act as a nucleation site of spherulitic barite (Figure 3g–h, and see additional data in González‐Muñoz et al, 2012, Stevens et al, 2015, Torres‐Crespo et al, 2015).…”

Morphology of Barite Synthesized by In-Situ Mixing of Na2SO4 and BaCl2 Solutions at 200 °C

“…where a(Ba 2+ ) and a(SO 4 2− ) are the activities of Ba 2+ and SO 4 2− , respectively, K sp is the solubility product of barite. For barite, K sp is 9.82 × 10 −11 at 25 • C [8]. Previous work has demonstrated that at high reagent supersaturation ratios (the natural logarithm of supersaturation ratio, lnS = 16.97), a large number of very small spherical nanoparticles will be formed.…”

“…Early Earth's marine environments were anoxic and sulfate deposits prevailed, resulting in barite as the dominant or the only sulfate mineral within bedded sulfate deposits older than 2.4 Ga [3][4][5][6][7]. Due to its high density and strong resistance to chemical weathering, barite is present throughout Earth's history and has the potential to preserve a record of conditions attending formation, which could be useful for interpretations of Earth's ancient rocks and paleoenvironments [8].…”