This is the rock name to remember when you find a hard, nondescript rock that looks like it could be slate
but doesn't have slate's trademark cleavage. Argillite is a low-grade metamorphosed claystone
that was subjected to mild heat and pressure without strong directionality. Argillite does have a glamorous side that slate can't match: it is also known as pipestone
when it lends itself to carving. The American Indians favored it for tobacco pipes and other small ceremonial or decorative objects.