2-3cm rough Smokey Quartz
About Smokey Quartz from My Crystalpedia.org:
“Stone of Endurance”
Smoky Quartz is one of the most unique and powerful, yet most efficient grounding stones. It rules over the root chakra and helps one to re-establish a connection to the physical world. This crystal is perfect for someone who seems to have their head stuck in the clouds or have lost touch to the physical side of life. Just go ahead and give them a Smoky Quartz. It t will help them regain mental clarity all while repairing their cellular structure/energy body.