ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
UnevenWalter Schumann, Gemstones of the world (2001) More from other references, UnevenWalter Schumann, Gemstones of the world (2001) More from other references, Uneven