Ultrathin ternary 2D materials have recently gained significant attention in the context of tailoring physical properties of materials via stoichiometric variation, which are crucial to many applications in optoelectronics, thermoelectrics, and nanophotonics. Herein, sulfide mineral getchellite is identified as a new type of ternary layered material and large-area getchellite thin flakes are prepared through mechanical exfoliation. The highly anisotropic linear and nonlinear optical responses of getchellite thin flakes facilitated by the reduced in-plane crystal symmetry are reported, including anisotropic Raman scattering, wavelength-dependent linear dichroism transition, and anisotropic third-harmonic generation (THG). Furthermore, the third-order nonlinear susceptibility for getchellite crystal is retrieved from the thickness-dependent THG emission. The demonstrated strong anisotropic linear and nonlinear optical properties of van der Waals layered getchellite will have implications for future technological innovations in photodetectors, optical sensors, nonlinear optical signal processors, and other on-chip photonic device prototypes.