My land is composed almost entirely of metamorphized basalt about 250 million years old, but there are two exceptions to this. I found sandstone and shale at several locations. At first, I dismissed these as aliens dropped here by people, but when I found more samples at three different locations more than 50 meters apart, I realized that these truly are native rocks. Here are the samples:
Shale with inclusion
Side view of shale
An inclusion in a different piece of shale
The shale is quite soft: between calcite and fluorite. It is also quite friable, although I don’t know how to measure its friability.
Sandstone
Magnified sandstone
The sandstone is also soft, coming in between fluorite and apatite. I also found some mudstone in the same general area some years ago, but dismissed it as a weirdo and have since lost it.