Charlesite is a sulfate mineral of the ettringite group. Charlesite was named in 1945 after Dr. Charles Palache, a mineralogist and professor at Harvard University for his work on minerals. This mineral is extremely rare, and when it is found it is usually in crystal form. Its crystals are soft and hexagonal, and can vary in color. Colors can range from clear to white, or even pale yellow or pink. The brittle mineral's Mohs hardness is 2.5 with a specific gravity of 1.79. Though transparent to the eye, the mineral has a white streak.