chlorite

kloriitti puhekieltä A dark green mineral resembling serpentine, being a mixed silicate of magnesium, iron and aluminium.
2004, (w), The Earth, Folio Society 2011, p. 177:

They have been heated enough to impart a delicate blue-green hue, which is because of the abundance of the ‘low-grade’ metamorphic mineral, chlorite.