Strange Sand

A couple of months ago while planting my cassava stems with a friend in the farm, I stumbled upon these sand. It's a fresh sand with some liquid making it shine.

Initially, I thought it was something else but I took time to study them, I noticed they were sand from the soil. There were insects in the soil pushing them out as I suggest they were building underneath.

Could there be any other chemical elements that these insects poured on these sand? Cause they get stiffen when dried. Here, it looks like chocolate and entirely different from the top soil.