Greenschist

[1] Greenschist is a general field petrologic term for metamorphic or altered mafic volcanic rock.

[2] Greenschist is defined by the presence of the minerals chlorite, epidote, or actinolite, which give the rock its green color.

[4][5] Greenschist may also contain albite and often has a lepidoblastic, nematoblastic or schistose texture defined primarily by chlorite and actinolite.

Chlorite and to a lesser extent actinolite typically exhibit small, flat or acicular crystal habits.

Temperatures of approximately 400 to 500 °C (750 to 930 °F) and depths of about 8 to 50 kilometres (5 to 31 miles) are the typical envelope of greenschist facies rocks.

A form of chlorite schist was popular in prehistoric Native American communities for the production of axes and celts, as well as ornamental items.

In the Middle Woodland period, greenschist was one of the many trade items that were part of the Hopewell culture exchange network, sometimes transported over thousands of kilometers.

During the time of the Mississippian culture, the polity of Moundville apparently had some control over the production and distribution of greenschist.