Ran across this :
https://empressfurniture.com/properties-of-tanzanian-timber/
From the hardness you mention, I wonder if it might be teak vis-a-vis
"the highest quality teak wood will have a golden brown colour. The real teak wood has a long, straight grain. The low-quality teak wood will feature larger knots"
But (assuming) it was found on the side of the mountain itself, this line about Podocarpus usambarensis makes it a possibility too.
"Podocarpus usambarensis is a tree growing in highland rain forests, in altitudes of 950-2,700 m. (ed note - Kiliminjaro goes up to 5800 meters) In Tanzania it is found in Kilimanjaro, Pare, Usambara, Iringa, Mbulu, Njombe and Uluguru .... There are two varieties in Tanzania: P. usambarensis war usambarensis found in highland areas"
Searching for that later term comes up with this :
https://www.conifers.org/po/Afrocarpus_usambarensis.php
This line leapt out :
"Bark dark brown turning gray with age, forming small angular plates, flaking."
And there's about 4 others on the original link, and the wood database has two listings for woods from Tanzania -
https://www.wood-database.com/leadwood/ and
https://www.wood-database.com/african-crabwood/