Vote for your favorite mineral in #MinCup26! - Sphalerite vs. Anorthite Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
Dunn (1995) gives the following account:
“Fine, yellow, euhedral norbergite crystals, up to 25 mm in clusters to 3 x 2 x 2 cm, were found in the Franklin Quarry in 1982 and have the tabular habit figured by Palache. In this occurrence, norbergite is associated with calcite, hercynite, and phlogopite."
Franklin Quarry, Franklin, Sussex County, New Jersey, USA