Bought 100 lbs of BDBS for my soon to be set up 60G last night based on the opinions here that it was a good substrate. What caught my eye was a sticker that had health warnings on it. This gave me pause, so I found the MSDS sheets for Black Diamond on the manufacturer website. Turns out that they use iron oxide for some media branded Black Diamond, see MSDS here: http://www.us-minerals.com/wp-content/uploads/2015/04/Iron-Silicate-SDS-1.3-2015.pdf They also use coal slag and use the same brand name: http://www.us-minerals.com/wp-content/uploads/2015/03/Coal-Slag-SDS-2.4-2015.pdf The bags I purchased do not say which abrasive is actually contained inside the bag... I am wondering if this may explain why some members disagree on the consistency of the product. Perhaps one material is sharper than the other? The product page say both products are chemically inert... anyone have any thoughts?