| Eosphorite | |
| Category: | Phosphate mineral |
| Formula: | MnAl(PO4)(OH)2·H2O |
| Imasymbol: | Eos[1] |
| Strunz: | 8.DD.20 |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Cmca |
| Unit Cell: | a = 10.455(1), b = 13.501(2) c = 6.928(1) [Å]; β = 90°; Z = 8 |
| Color: | usually pale brown, golden brown, also medium brown to dark brown; occasionally pink, rose red |
| Habit: | Prismatic in radiating sprays or spheres, massive; twinned pseudo-orthorhombic |
| Twinning: | May be observed on and |
| Cleavage: | Poor on |
| Fracture: | Subconchoidal to uneven |
| Mohs: | 5 |
| Luster: | Vitreous, resinous |
| Streak: | White |
| Diaphaneity: | Transparent to translucent |
| Gravity: | 3.06 – 3.08 |
| Opticalprop: | Biaxial (-) |
| Refractive: | nα = 1.628 - 1.639 nβ = 1.648 - 1.664 nγ = 1.657 - 1.671 |
| Birefringence: | δ = 0.029 - 0.032 |
| Pleochroism: | Visible: X = yellow; Y = pink; Z = pale pink to colorless |
| 2V: | Measured: 50° |
| Alteration: | Oxidizes to brown or black |
| References: | [2] |
Eosphorite is a brown (occasionally pink) manganese hydrous phosphate mineral with chemical formula: MnAl(PO4)(OH)2·H2O.[3] It is used as a gemstone.[4]
Eosphorite crystallizes in the monoclinic crystal system. It forms slender prismatic crystals which often form radiating or spherical clusters. The crystals often show pseudo–orthorhombic forms due to twinning.[2]
Eosphorite forms a series with childrenite, the iron rich member, with divalent iron replacing most of the manganese in the crystal lattice. The two endmembers are isostructural but differ in their properties, such as crystal habit, coloration, and optical properties.
It was first described in 1878 for an occurrence in the Branchville Mica Mine in Branchville, Fairfield County, Connecticut, US. Its name is derived from the Greek έωσφορος for "dawn-bearing," because of its pink color. It occurs worldwide typically as a secondary mineral in phosphate rich granitic pegmatites in association with rhodochrosite, lithiophilite, triphylite, triploidite, dickinsonite, albite, cookeite, apatite, beryllonite, hydroxyl-herderite, and tourmaline.[2] An attractive combination of eosphorite and rose quartz occurs at Taquaral, Minas Gerais, Brazil.[5]