2. Basic components: minerals

The main types are:

Phytoliths. They are small bodies, generally the size of silt (< 1 mm), formed of opal and originating inside plants. They are easily distinguished as they are isotopes, with a negative relief and with specific shapes, sometimes very irregular, and with fine inclusions of carbon.

Diatoms. They are unicellular plants with an external skeleton of opal (black with crossed polarizer and analyser). They have shapes with very spectacular symmetries.

Sponge spicules. They are cylindrical bodies with a small channel inside.

Radiolarians, shells, crystals of differents calcium salts and bones.

For all of them there is a description of their: shape, abundance, internal characteristics and alteration.