Almost unique

I just did a Google search of the word argiferous. It produced four results and three of them are links to this blog. The genuine use of the word appears on a site which tells the story of mining in Leadhills and Wanlockhead. When I say genuine use what I really mean is typo since argiferous is just a word I made up. I think what they mean is argilliferous which is an adjective for a type of rock that contains clay.