Haidingerite is a calcium arsenate mineral with formula Ca(AsO3OH)·H2O. It crystallizes in the orthorhombic crystal system as short prismatic to equant crystals. It typically occurs as scaly, botryoidal or fibrous coatings. It is soft, Mohs hardness of 2 to 2.5, and has a specific gravity of 2.95. It has refractive indices of nα = 1.590, nβ = 1... Found on http://en.wikipedia.org/wiki/Haidingerite
Hai'ding·er·ite (hī'dĭng*ẽr*īt) noun (Min.) A mineral consisting chiefly of the arseniate of lime; -- so named in honor of W. Haidinger , of Vienna. Found on http://www.encyclo.co.uk/webster/H/5