U.S. Borax refined borates are sourced from one location: Our Boron, California mine. The boron in this deposit comes primarily from tincal and kernite, which are calcium-free sodium borates.
Why does this fact matter? Because excess calcium can cause boron-deficiency symptoms in plants.
Borates that contain colemanite or ulexite—calcium-borate minerals found in many raw or lower-quality boron products—often contain high levels of calcium, even after refinement. The difference is clear—literally.