My dad’s neighbor took this (see glove). I wasn’t sure if the white powder was an additive or breakdown of the rock, and hoped it wouldn’t hinder plant growth. Metamorphic rock is generally resistant to weathering, but they are jumbled a lot in transport.
In Horticulture at Bethel College, Professor Russ Johnson taught us that adding sand + humus to clay can help make loam; but when I bought my house and added Home Depot (playground) sand, it killed the bushes because it had salt from the beach. I wouldn’t want the little succulent gardens to have, like anthrax, in them.