Sitting atop a matrix of dark black stone are some large, sharp alum crystals to 2" on this colorful lab-grown specimen from Poland. The crystals are a rich, emerald green color, so they contrast very nicely with the almost black matrix. The crystals have intricately skeletal interiors (one smaller one is gem clear), are very geometric octahedrons, with smooth, shiny faces, good clarity, and sharp corners. The luster is good, and there is no damage to this lab-grown specimen.