charlesite

{{infobox mineral | name = Charlesite | category = Sulfate mineral Ettringite group | boxwidth = | boxbgcolor = | image = Charlesite3.jpg | imagesize = 260px | alt = | caption = Charlesite from N'Chwaning mines, Kalahari manganese fields, Northern Cape Province, South Africa | formula = Ca6(Al,Si)2(SO4)2B(OH4)(O,OH)12·26H2O | IMAsymbol = Chrl | strunz = 7.DG.15 | dana = 32.4.4.1 | system = Trigonal | class = Ditrigonal pyramidal (3m) (same H-M symbol) | symmetry = P31c | unit cell = a = 11.16 Å, c = 21.21 Å; Z = 2 | color = Colorless, white, rarely pale yellow, rarely pink | colour = | habit = Prismatic, hexagonal dipyramidal crystals | twinning = none | cleavage = Perfect on {10bar10} | fracture = Irregular/Uneven | tenacity = Brittle | mohs = 2.5 | luster = Vitreous on cleavage and fracture surfaces | streak = White | diaphaneity = Transparent | gravity = | density = 1.77 g/cm3 | opticalprop = uniaxial (-) | refractive = nώ = 1.492(3) n∈ = 1.475(3) | pleochroism = Nearly colorless to pale golden yellow | dispersion = | extinction = | length fast/slow = | fluorescence= there is weak violet or weak green short wave ultraviolet radiation | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = | alteration = | references = }} 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 (but not gem) 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.

== Occurrence ==