We propose a new non-Cartesian sampling scheme based on a 3D cones k-space trajectory. The design framework uses a cones coordinate system that uniquely represents a point in 3D k-space with a rotation of a spiral that resides on a conic surface. The new trajectory is obtained by discretizing the proposed coordinate system. Incorporation of a variable-density spiral improves the sampling efficiency. Simulations and phantom studies demonstrate the improved efficiency of the new scheme compared to the conventional cones design.