A process of preparing a biogenic silica comprising the steps of incinerating a silica bearing organic source at a temperature up to 1200.degree. C. and allowing the incinerated silica organic source to cool; adding the incinerated and cooled silica bearing organic source to an alkaline solution that has either been preheated to a temperature up to about 65.degree. C. or to be heated with the added organic source to a temperature up to about 65.degree. C., the alkaline solution being contained in a vessel and having a pH up to 14; applying heat so that the added organic source and the alkaline solution in the vessel are at a temperature between 100.degree. C. and up to about 300.degree. C. for 1 to 4 hours, thereby forming an aqueous biogenic silica and undissolved impurities derived from the added organic source; and extracting the aqueous biogenic silica from the vessel. The extracted silica can be solidified into a solid form.