Plants, Mushrooms, Forage, Wander, Rocks

I've been testing around Boston for purities of items found on the ground. I noticed that maybe the purity of items change not by type (rock, mushroom or plant) but rather by each item individually. Meaning that autumn grass, Milkweed Roots and Oakworth, each gave different purity element in the same area. I know it depends on my proficiencies too, but I have some questions.
Is there a difference between wander and foraging when looking for items?
Does purity depend on item type such as rock or plant, or is it individual for each item?
How much do proficiencies influence this?
Does it affect animals?
I was planning on putting together a small file that helps me find different items with different purities...but maybe this means I will need to put this together for each single item.
Is there a difference between wander and foraging when looking for items?
Does purity depend on item type such as rock or plant, or is it individual for each item?
How much do proficiencies influence this?
Does it affect animals?
I was planning on putting together a small file that helps me find different items with different purities...but maybe this means I will need to put this together for each single item.