Originally Posted by
Pratt
In my experience, slippery mud is clay. Sand is small quartz grains. Crushed stone may be soft limestone, or hard granite. Clay and limestone are soft enough for the chain and gears to handle. Quartz and granite, on the contrary will eat the drive train.
YMMV
This stuff was wet and light tan colored. It washed down from a construction site uphill from the trail. It was just fine silt. I managed to clean most of it but I missed some that had been sprayed up under the seat.