These stacks are plain, brown beach sand magnified 7.5x times. The sand happens to be from the five D-Day (June 6, 1944) landing beaches on the Normandy coast that were coded as "Utah", "Omaha", "Gold", "Juno", and "Sword". I "smuggled" back to the USA a few ounces of sand from each of these beaches while touring all of them during a business trip to France in the late 1990's. I recently rediscovered the samples in a closet and decided to do some stacking shots of this sand to see what the particles really look like. (Inspiration for this came from Beatsy's Oct 10 post. Nice work, dude.) The stacks took from 62 to 132 shots.
What is interesting about the sand is the unexpected range of colors found in the tiny sand particles. Orange, red, and yellow particles predominate in all the samples but these colors combine with particles in the blue and green spectrum to cause the sand to have a brown-ish, tan-ish, semi-neutral color that is very dull, at least when viewed from a distance. Of course, it's a whole different world at the “grains of sand” level. All the particles in the images are correctly sized relative to each other, since the images are all at the same magnification and are not cropped.
This hobby is always full of surprises.
Here are the samples viewed normally. Note the differences in coarseness.

Utah beach. Somewhat fine sand but with some coarse particles.

Omaha beach. Very fine sand and very uniform. Somewhat like 200-grit abrasive.

Gold beach. About 50/50 mixture of coarse and fine sand.

Juno beach. Very coarse sand. Has somewhat fewer dark-red particles than the samples from the other beaches.

Sword beach. Very coarse sand, similar to Juno, but with a wider range of colored particles. Particles from this beach seem somewhat more “rounded” (weathered) than sand from Juno.

Thanks to everyone on this forum.