I visited my parent's house two weekends ago, and found yet another earth pigment! My dad had dug a very deep hole with his excavator, in hopes that he could make an artificial pond. No such luck. But what he thinks might be sandstone (too soft for it in my opinion) I think might be related to ochre.
Here's a couple of comparison shots between the three tones I've found on his land so far. The brown/red is his normal soil, the reddest sample is that same soil after a bonfire has taken place on top of it, and the yellow/ochre is in his orchard, starting at about 4 feet deep in pockets, and showing up as deep as the 12' or so hole that he dug.
By the way, I was able to see different colors in this sample, like sedimentary layers. Maybe in a few thousand years, it would become a sedimentary rock.
Here's what it looks like in a standard slurry test (my attempt to get the fine particles separated out from the coarse ones with water. It settled in under an hour, very, very fast for such a test!). There's a lot of sand in there. I crushed it first in my mortar, and I think the crushing might have affected the color a bit. It's redder now. We'll see how it handles when it dries.