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.