Their frustules (shells) are nanostructured pure amorphous silica, which gives them interesting and possibly useful optical properties:
https://pubs.rsc.org/en/content/articlelanding/2020/fd/d0fd0...
https://royalsocietypublishing.org/doi/10.1098/rsfs.2018.003...
Some pictures of the frustrules, with some words and diagrams too:
https://www.frontiersin.org/articles/10.3389/fmars.2018.0012...
https://zerok.com/assets/slides/MM2022_Vendor_Tutorial.pdf
slide 28
Background: This is SIMS data (https://en.wikipedia.org/wiki/Secondary_ion_mass_spectrometr...). We have a new instrument can perform these analyses at much higher resolution than has been possible historically.
Since diatoms exhibit movement, reproduction, production of food, metabolism, etc they are characterized as living organisms.