Spheres can form squares
How to make fit a square peg into a round hole? If you are using spherical micrometer sized particles that are colloids and have an oil water interface you might want to adjust the surface tension. You can minimize the surface of these spherical particles to make a more compact square like stackable structure by placing these particles on a curved oil-water surface e.g. the meniscus. The same effect is observed in your bowl of Cheerios (cereal) and is called the Cheerio effect. It has been suggested to be used to see the self assembly of small structures (likely how evolution first started in reactions of dirty volcanic ponds).