Focus on Sedimentary Environments

Sombrero Beach, Marathon, Florida Keys, USA

Identifying carbonate grains

This is not an easy task! Many of these grains are difficult to identify, and almost none show their original shape, as they have been broken during sediment transport. Others have been extensively altered by microbial micritization.

The following may be identified:

occasional small gastropods
mollusc shell fragments, some with borings
calcareous green algae
calcareous red algae
large benthic foraminifera
coral
echinoid spines

As well as skeletal carbonate fragments, quartz grains are present

Move the cursor over the image excerpt below to see grain identifications: works best in Internet Explorer
(if labels do not appear, move the cursor outside the image, then back again)


	Thin section of beach sand, viewed in plane-polarized light