Leakey's fascination with stone tools stemmed from when he was sent a book at age 12 as a Christmas present.
Fascinated by the descriptions of flint stone tools he set about looking for his own. In the book flint was described as being dark, glassy and sharp.
Below is a typical flint handaxe.
As luck would have it Kenya has little of the flint type rocks but borders the Great Rift valley. There is plenty of volcanic activity there and volcanoes produce obsidian.
Obsidian provides a fine material for tool manufacture since it delivers a finer edge than broken glass.
Above is the type of fine stone tools that can be made with obsidian. This type is typically from the Americas. Africa's tools being very much older differ substantially in style and many of the most common ones are far less recognizable.
He soon found many sharp black flakes in the nearby surrounds but many were skeptical until he met up with Arthur Lovebridge of the Nairobi Museum.
Lovebridge confirmed that some of his collection were indeed tools and that they were not made from flint but of obsidian. From then on Leakey was hooked.
Handaxes are more common in Africa and some very fine specimens can be found made from obsidian and are plentiful where they occur.