Siliceous ooze is a siliceous pelagic sediment that covers large areas of the deep ocean floor. Siliceous oozes consist predominantly of the remains of microscopic sea creatures, mostly those of diatoms and radiolarians. Sometimes siliceous oozes also contain silicoflagellates and the spicules of sponges.

• Diatoms are golden-brown algae that construct an opaline silica microscopic shell that is known as a "frustule".
• Silicoflagellates are a minor group of marine algae that construct microscopic shells composed of opaline silica.
• Radiolarians are marine protists that also construct microscopic shells composed of opaline silica and are distant relatives of the foraminifera.