The main sources of silica in oceans are: 1) Continental weathering of rocks releasing silica into rivers at 13 ppm. 2) Submarine volcanism and hydrothermal vents also contribute silica. 3) Low-temperature alteration of oceanic basalt and sediments on the seafloor leads to formation of clay minerals, zeolites, and glauconite, enriching pore fluids with silica. Despite these contributions, the average dissolved silica in oceans is low at only 1 ppm due to its low solubility.

1. SOURCES OF SILICA
Silica (13 ppm) as H4Si04 in river water through
continental weathering
Submarine volcanism and associated Hydrothermal
emanations
Halmyrolysis (Early Diagenesis)
• Low-temperature alteration of oceanic basalts and
detrital silicate particles on the seafloor
•Olivine in Basalts change to smectite clay minerals
•Formation of Zeolite, Palagonite,,,Glauconite
(Weathering of feldspars, Mica ).
Pore fluids of pelagic sediments enriched in silica on the
sea floor
Despite these contributions, average dissolved silica
content in ocean is just 1ppm.

2. Source of silica and Diagenesis
Source ; Sam Boggs Jr.

3. SILICA SOLUBILITY
 Differs for different silicate minerals
 At 25C and normal ocean pH ( ~7.8-8.3) condition;
• Quartz solubility – 6 to 10 ppm
• Amorphous Silica (Opal) sol. – 60 to 130 ppm
 Factors affecting Solubility of Silica
 pH
 Solubility increases with increase in pH
 Rises sharply above 9 pH value
Temperature
 Solubility increases with increase in temperature in a linear
fashion.
Pressure
 Solubility increases with increase in pressure

4. Silica solubility as a function
of (A.) pH & (B.)Temperature
A. Upper dashed line shows solubility of amorphous silica – 120
ppm at 8 & sol. of quartz – 6 ppm at <= 7
B. Dashed line and Solid line shows the variation