Clear Quartz - Tumble stone (Gemstone) - 4 sizes to choose from. 
Price is from €3 to €8 depending on the size of the crystal. 
Clear quartz crystals dispel feelings of negativity while encouraging positive feelings and thoughts, Clear quartz gemstones enhance awareness and improves one's perceptions. Energy levels are increased, thought processes are improved and clarified. 
Clear quartz is also known as Rock crystal and the master crystal.