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!
Crystals usually in aggregates (up to 15 cm) typically well terminated but very brittle and easily damaged due to incipient fractures and metamict nature. Fractures conchoidally with lustrous, pitch-black surface. Commonly associated with columbite-(Fe) that has a duller luster especially on the fracture face. Coated with clays from altered surrounding feldspars that are reddish colored, and thin muscovite, both can be removed with micro-blasting using soft abrasive.
Habit:
radiating to subparallel prismatic groups with dome terminations
Colour:
black
Quality for species:
Excellent - world class for species or very significant. (!!)
Spinelli prospect, Glastonbury, Hartford County, Connecticut, USA