Many so called natural vitamins are made from horrible substances. All the vitamin B-12, cyanocobalamin, on the market is made from either ground up toxic cow livers or activated sewage sludge. These cow livers are overloaded with steroids and antibiotics, and the pesticides the cow assimilates while eating. The sewage sludge is just that, fecal matter. In today's environment of depressed immune diseases I can think of hundreds of reasons that these materials would be a health risk, not benefit.
All minerals used in nutrient manufacture are basically dirt.
The iron, calcium, zinc etc. are just mined ore, pulverised and powdered to a fine dust. This doesn't make it any easier to assimilate. Some calcium is made from ground up oyster shells. This reminds me of when I was a kid watching the Three Stooges fix dinner, they would throw the oysters away and try and chew the shells. We all laughed at them and now we are doing the same thing.