diatoms are fairly easy to collect in the wild, from moss and other moist areas of your yard. https://www.mccrone.com/mm/the-collecting-cleaning-and-mounting-

diatoms are fairly easy to collect in the wild, from moss and other moist areas of your yard. https://www.mccrone.com/mm/the-collecting-cleaning-and-mounting-of-diatoms/ https://www.mccrone.com/mm/the-collecting-cleaning-and-mount... http://www.microscopy-uk.org.uk/mag/artjun15/sb-Diatom-Arranging.pdf http://www.microscopy-uk.org.uk/mag/artjun15/sb-Diatom-Arran... they are quite small and mostly transparent which makes good observation challenging.