folium(n = noun.object) - a thin layer or stratum of (especially metamorphic) rock;
is a kind of formation, geological formation
Derived form adjective foliaceous₃

1.  A leaf, esp. a thin leaf or plate. [1913 Webster]

2.  A curve of the third order, consisting of two infinite branches, which have a common asymptote. The curve has a double point, and a leaf-shaped loop; whence the name. Its equation is x3 + y3 = axy. [1913 Webster]