Each impact-resistant 2 mL tube contains 0.8 mm zirconium silicate beads. Lysing Matrix K tubes have brown caps and are found in the GeneCleanTM for Ancient DNA Kit. Zirconium oxide has very high density and high tensile strength and hardness, and is effective at breaking very tough and hard samples. The small spheres are also effective in breaking fungal spores, cysts, and yeast polysaccharide capsules.