David Byers Collection This is a very nice dioptase with large brilliant dark green crystals on white calcite matrix. One of the most classic of Tsumeb minerals. The huge main crystal, nearly 3 cm from tip to tip, is laying on its side and has just a bit of damage at the back near the edge of the specimen. The damage and the fact that the main crystal is not standing up from the matrix keep this from being a world-class miniature.