The difference between white and grey diatomaceous earth is that the grey DE comes from a deposit that also contains other natural substances such as montmorillonite (also known as calcium bentonite). White DE on the other hand is pure diatomaceous earth.
The montmorillonite clay in the grey DE will not hurt your animals in fact, it contains micro and macro minerals that are important for their health.
The montmorillonite is not added to the product but rather it occurs naturally as part of the diatomaceous earth deposit and is very beneficial. White DE contains more silica (amorphous silica - the good stuff) however beyond a certain point extra silica is only filler and it is more beneficial for your animals to have a product that contains the extra micro and macro minerals that are found in montmorillonite.
Thanks MelissaHJ - that is very helpful! I feel much better (and wiser) now.
This BYC forum is so helpful. While I enjoy researching stuff, it can get very time-consuming; I read one article which leads to another and then another, etc.
So its great to be able to put a question out there and benefit from other peoples research and experience. Thanks BYC members