charlesite is a sulfate mineral of the ettringite group. charlesite was named in 1945 after dr. charles palache mineralogist and professor at harvard university for his work on minerals. this mineral is extremely rare, and when it is found it is often in crystal (but not gem) form. its crystals are soft hexagonal, that can vary in color. colors can range from clear to white, or even a 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.