Amorphous silicas having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500.mu. and a thickness of about 50 A to about 1.mu., the length being at least about 10 times the thickness, the amorphous silicas being in the form of primary particles, secondary...http://www.google.fr/patents/US4230765?utm_source=gb-gplus-shareBrevet US4230765 - Novel amorphous silica, and products thereof
