Magnesium is found in green rocks and plants tend to be green because the pigment/protein (chlorophyll) involved in photosynthesis uses magnesium in a way similar to iron in hemoglobin. (Chemistry for Biologists, Inorganic Ions, rsc.org). Magnesium is important in human biology for many other enzymatic reactions and in cellular membrane transport. (Symptoms of magnesium deficiency and food or supplement sources.)
Disclaimer: Information provided for educational purposes within the guidelines of fair use.