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

**Chunyao Wang 1,2, Li Zhou 3,4,\*, Shuai Zhang 1,2, Li Wang 1, Chunwan Wei 5, Wenlei Song 6,7, Liping Xu <sup>8</sup> and Wenge Zhou 1,\***


**Abstract:** Barite is an abundant sulfate mineral in nature. Especially, the variety of morphologies of barite is often driven by the mixing of Ba-bearing hydrothermal fluid and sulfate-bearing seawater around hydrothermal chimneys. In order to better understand the factors affecting the morphology and precipitation mechanism(s) of barite in seafloor hydrothermal systems, we synthesized barite by a new method of in-situ mixing of BaCl2 and Na2SO4 solutions at 200 ◦C while varying Ba concentrations and ratios of Ba2+/SO4 <sup>2</sup>−, and at room temperature for comparison. The results show that barite synthesized by in-situ mixing of BaCl2 and Na2SO4 solutions at 200 ◦C forms a variety of morphologies, including rod-shaped, granular, plate-shaped, dendritic, X-shaped, and T-shaped morphologies, while room temperature barites display relatively simple, granular, or leaflike morphologies. Thus, temperature affects barite morphology. Moreover, dendritic barite crystals only occurred at conditions where Ba2+ is in excess of SO4 <sup>2</sup><sup>−</sup> at the experimental concentrations. The dendritic morphology of barite may be an important typomorphic feature of barite formed in high-temperature fluids directly mixing with excess Ba2+ relative to SO4 <sup>2</sup>−.

**Keywords:** Barite; hydrothermal synthesis; typomorphic characteristics; in-situ mixing solutions at high temperature
