Pumpellyite

Pumpellyite is a group of closely related sorosilicate minerals:

Pumpellyite crystallizes in the monoclinic-prismatic crystal system. It typically occurs as blue-green to olive green fibrous to lamellar masses. It is translucent and glassy with a Mohs hardness of 5.5 and a specific gravity of 3.2. It has refractive indices of n_α=1.674–1.748, n_β=1.675–1.754 and n_γ=1.688–1.764.