Structure of silica in Equisetum arvense.

Silicified regions in the stem and leaf of the horsetail Equisetum arvensewere studied by scanning and transmission electron microscopy. The silica was present as a thin layer on the outer surface with variation in the size of this layer depending on the part investigated. There was a dense arrangement of silica spheres with some density fluctuations. A loose arrangement of silica particles with variation in their size was found beneath this dense arrangement suggesting the agglomeration of silica. An electron diffraction pattern showed the presence of amorphous silica, with the short range order being comparable to that of silica from other chemical sources. The medium range order shows the presence of silica with a high inner surface. SAXS measurements correlate with the particle size observed in TEM, and provide values for surface fractals. A new method of plasma ashing to remove the organics is also described.