Phytolith
Some plants can take up silica in the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. After these plants decay, silica is redeposited in the soil in the form of phytoliths (from Greek, "plant stone"), which are rigid, microscopic structures of varying sizes and shapes. Although some use "phytolith" to refer to all mineral secretions by plants, it more commonly refers to siliceous plant remains. Mineralized calcium secretions, commonly used for diagnostic research in cacti remains, are composed of calcium oxalates.
Read more about Phytolith: History of Phytolith Research, Development in Plants, Archaeology, Palaeontology, Carbon Sequestration, See Also