In 1993 we visited Kanye, up the road from Gaborone, and walked in the hills above the settlement. There are some stoneworks dating from the 18th century or so in this area which are difficult to interpret. Whilst walking around I picked up the stone in the photos below.
I took the stone into work and asked an archaeology lecturer about it. He had a look at it and said that it was a stone age flake reject, and it could have been worked up to half a million years ago.