This is a large specimen of green micro-malachite on a 3-dimensional matrix of heavily oxidized copper, from the great Tsumeb locality. You can also see little creamy cerussites atop the malachite, so this is a very interesting association piece that shows the richness of this mine (copper, lead and other metals made it a richly rewarding mine for many decades, and it turned out a dizzying array of secondary minerals). Rare association!