The Picket Fence Studios Thunderstorm Gem Mix are high-quality flat-back gemstones. Comes in compact cases with clear lids, ready to store and use as soon as they arrive, and they even let you peek in from the side to grab the mix you want easily from a stack. The lids are flat, so the containers can be stacked on a shelf or in a drawer. Each compact contains a mixture of 3 colors and 4 different sizes, ranging from 2-4mm. The stone weight is 12-13 grams, with approximately 750 stones. These vibrant, iridescent black, silver and clear gems add a sparkly and elegant touch to any project.