chemical properties, 2D materials have long been the forefront of fundamental research and applications in optics and many other fields. [1][2][3][4] For instance, many efforts have been devoted to explore physical paradigms under 2D limit and enable novel optical devices, such as exciton-resonance-enabled lens, [5,6] wideband tunable mode lockers, [7,8] as well as photodetectors and harmonic generators in terahertz regime. [2,9] Noteworthy, together with recently reported 2D ferromagnets, [10][11][12] 2D materials based magneto-optics have attracted great attentions nowadays. Categorized by the interaction between material and incident light under magnetic field, four main magnetooptical effects are investigated commonly, namely the Zeeman effect, Faraday effect, magneto-optical Kerr effect, and Cotton-Mouton effect, in which 2D materials are recognized as promising matters. [13] Among these four magneto-optical effects, the Cotton-Mouton effect is of great benefits for transmitted light modulation in a see-through manner, with the potential applications ranging from sub-micron-scale dynamic light modulators to meter-scale displayable windows in future society. [14,15] The current electro-optical technologies based on liquid crystals face Liquid crystal devices using organic molecules are nowadays widely used to modulate transmitted light, but this technology still suffers from relatively weak response, high cost, toxicity and environmental concerns, and cannot fully meet the demand of future sustainable society. Here, an alternative approach to color-tunable optical devices, which is based on sustainable inorganic liquid crystals derived from 2D mineral materials abundant in nature, is described. The prototypical 2D mineral of vermiculite is massively produced by a green method, possessing size-to-thickness aspect ratios of >10 3 , inplane magnetization of >10 emu g −1 , and an optical bandgap of >3 eV. These characteristics endow 2D vermiculite with sensitive magneto-birefringence response, been several orders of magnitude larger than organic counterparts, as well as capability of broad-spectrum modulation. The finding consequently permits the fabrication of various magnetochromic or mechanochromic devices with low or even zero-energy consumption during operation. This work creates opportunities for the application of sustainable materials in advanced optics.
