The Collaborative International Dictionary
mock lead
Blende \Blende\, n. [G., fr. blenden to blind, dazzle, deceive, fr. blind blind. So called either in allusion to its dazzling luster; or (Dana) because, though often resembling galena, it yields no lead. Cf. Sphalerite.] (Min.)
A mineral, called also sphalerite, and by miners mock lead, false galena, and black-jack. It is a zinc sulphide, but often contains some iron. Its color is usually yellow, brown, or black, and its luster resinous.
A general term for some minerals, chiefly metallic sulphides which have a somewhat brilliant but nonmetallic luster.
Wiktionary
mock lead
n. (context mining English) blende