It is. It kinda makes a difference. If one used all clay entirely most plants would die because clay expands and contracts with moisture. A the bottom of every pond here is clay holding that water. There is a product we use to break it up called earth right. Some plants will break up those clay tables. My grandma used to use clay to fix injured corn plants so it can't be bad per se, but I don't use it as a grow medium. Next time maybe I'll just get some rocks from my driveway and save the confusion lol. On a side note, clay is nutrient rich, it "keeps" a bank of nutes. I live in a big ag area and we're loaded up with clay. I believe it came from a pre historic glacier, the one that carved out the Missouri river. We have interesting geology around here.