Twinning Impact on the Structure and Hypotheses on the Growth Mechanism of Kermesite: Insights from Yunnan, China

• Published in: Minerals (Basel) 2024-05, Vol.14 (5), p.505
• Main Authors: Yu, Hong, Wang, Denghong, Zhu, Zeying, Li, Wenyuan, Wang, Dong, Chen, Zhenyu, Li, Yike, Ke, Changhui
• Format: Article
• Language: English
• Subjects: Clusters; Crystal growth; Crystal structure; Crystals; Data collection; kermesite; mineral growth mechanisms; Mineral resources; Single crystals; Software; Symbionts; TEM; Triclinic crystals; twinning; Twinning (Crystallography); Unit cell
• ISSN: 2075-163X; 2075-163X
• DOI: 10.3390/min14050505

Kermesite (Sb2S2O), a needle-like unstable secondary oxysulfide, has made visible advancements in optimizing its triclinic crystal system through twinning discovery. However, research on twinning behavior at micro and nano scales, including its growth mechanisms and impact on kermesite morphologies, remains notably scarce. Our study focuses on kermesite crystal clusters from a private collection in Yunnan, China, confirming the chemical formula as Sb2S1.97O1.03 through EPMA. Single-crystal XRD yielded refined unit cell parameters (a = 8.153(5) Å, b = 10.717(7) Å, c = 5.796(3) Å; α = 102.836(10)°, β = 110.556(8)°, γ = 100.999(12)°), revealing space group P1¯ with Z = 4 and indicating twinning with a ratio of 27.4%. Remarkably, a Transmission Electron Microscope (TEM) provided the first direct observation of twinning in natural kermesite, revealing rotational twins with varying widths and lengths (ranging from 100 nm to several millimeters). Analysis and simulation elucidated that rotational twins, generated by a 180° rotation, align with the mineral’s elongation direction along the [Sb2S2O4]n chains (a-axis), challenging the conventional long-axis direction (b-axis) for crystal growth. This study proposes a symbiotic relationship between kermesite growth and twinning, suggesting that the observed X-shaped growth in crystal clusters results from the collaboration of single crystals (growing along b) and twins (growing along a) in the unit cell. These findings contribute to our understanding of kermesite’s structural complexities and the potential growth and formation mechanism of crystal clusters.