Black crystals of the rare mineral sadanagaite from Yuge Island, Inland Sea, Ehime Prefecture, Shikoku Island, Japan. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Sadanagaite
Sadanagaite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaCa₂(Mg₃Al₂)(Si₅Al₃)O₂₂(OH)₂.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Amphibole structural group.
Key properties: Mohs hardness 6; specific gravity 3.3; Very light brown streak; Vitreous luster; optically biaxial.
IMA symbol Sdg, IMA status: approved, named in 2002.
By contact metamorphism, producing banded skarns, under amphibolite to pyroxene hornfels facies conditions; from eclogites.
It is found associated with Vesuvianite, hercynite, sphene, ilmenite, apatite (Yuge Island, Japan); biotite, orthoclase, subsilicic ferroan pargasite (Nogo-Hakusan area, Japan).
The mineral was named to honor Professor Ryoichi Sadanaga of the Mineralogical Institute, University of Tokyo, Tokyo, Japan.