"Oxalic Acid Crystals During Precipitation" - James Dvorak 1975

This was the 1st place winner from the very first Nikon Small World Photomicrography competition, in 1975! It was made by transmitting polarized light with a Berek quartz wedge.

https://www.nikonsmallworld.com/galleries/1975-photomicrography-competition/oxalic-acid-crystals-during-precipitation