These are the crystals that I grew with my Quick, Easy Crystals activity. They are composed of magnesium sulfate. Why is magnesium sulfate also known as Epsom Salts?
Epsom, England was famous for its mineral water. In the late 1600's, Epsom had many health spas, where people soaked in the mineral water. In 1695, Nehemiah Grew was granted a patent for his method of extracting magnesium sulfate from that water. The result was known as Epsom salts.