I came across some black gravel I screened out for the color, but running a magnet found out it has iron in it. Now, question, is there any reason as to why a person can not use this , have heard that metal should not be used, but there is metal on the wheels, of rolling stock, locomotives, and the knuckle couplers have metal, in the meantime I will await for your answer before putting this stuff down

I realize that the use of analog trains is not permitted with this, but does that mean for the entire layout or just in the reverse loop section