The major dark colored minerals in a typical igneous rock will be biotite, hornblende, augite, and/or olivine: Biotite is easy because it forms perfect shiny black cleavages and can be peeled into flakes. It can be confused with hornblene, but hornblende does not flake. Hornblende and augite are often confused. Most reliable is cleavage: hornblende forms ~120°/60° cleavages whereas augite forms ~90° cleavages. In addition, hornblende tends to form very black and shiny cleavages, whereas augite forms duller black and not-very-reflective cleavages. Finally, hornblende tends to form long rectangular crystals whereas augite forms blocky crystals. Olivine is a glassy olive green and tends to form rounded, lumpy crystals.