Just about all NA Indian tribes kept slaves.

Some, like the B.C. Carrier Tribes, were only slaves, & did not 'take' or keep them, themselves.

The chunk of basalt I pictured above is/was not the point I found, but just a chunk of basalt to show the Conchoidal fracture characteristic of the rock.

When on the island of Hawaii last January, we learned that when Mauna Loa erupted under winter ice, it formed very finely grained rock, which made very good basalt for making the early Hawaiian's tools.

The liquid basalt forming at low and warmer elevations was quite porous, coarse grained and made poor tools. Be have both 'kinds' here as well.