The composition and physical properties of martian regolith are dramatically better understood compared to just a decade ago, particularly through the use of X-ray diffraction by the Curiosity rover. Because there are no samples of this regolith on Earth, researchers and engineers rely on terrestrial simulants to test future hardware and address fundamental science and engineering questions. Even with eventual sample return, the amount of material brought back would not be enough for bulk studies. Many existing Mars simulants were designed 10 or 20 years ago based on a more rudimentary understanding of martian surface materials. Here, we describe the Mars Global Simulant (MGS-1), a new open standard designed as a high fidelity mineralogical analog to global basaltic regolith on Mars, as represented by the Rocknest windblown deposit at Gale crater. We developed prototype simulants using the MGS-1 standard and characterized their basic physical properties, bulk chemistry, spectral properties, and volatile content. The MGS-1 based simulant compares favorably to rover and remote sensing observations from Mars, and offers dramatic improvements over past simulants in many areas. Modest amounts of simulant will be produced by the Center for Lunar & Asteroid Surface Science (CLASS) Exolith Lab to distribute to other researchers. By publishing the mineral recipe and production methods, we anticipate that other groups can re-create the simulant and modify it as they see fit, leading to a more sustainable model for simulant production and the possibility of extending the simulant for different regions on Mars or for different applications.