I figured "chat" was gravel or something from the context, but had never heard the term before. Maybe I'm the lone idiot, but in case anyone else is confused:
"Chat is a term for fragments of siliceous rock, limestone, and dolomite waste rejected in the lead-zinc milling operations that accompanied lead-zinc mining in the first half of the 20th century. [...] Although poisonous, chat can be used to improve traction on snow-covered roads; as gravel; and as construction aggregate, principally for railroad ballast, highway construction, and concrete production."
In general it just means small crushed gravel. It's usually white or tan. Not sure if it's always a remnant from mining or not. Does a good job on the trail though.
"Chat is a term for fragments of siliceous rock, limestone, and dolomite waste rejected in the lead-zinc milling operations that accompanied lead-zinc mining in the first half of the 20th century. [...] Although poisonous, chat can be used to improve traction on snow-covered roads; as gravel; and as construction aggregate, principally for railroad ballast, highway construction, and concrete production."
https://en.wikipedia.org/wiki/Chat_%28mining%29