From A Wiki in the Desert
A Slate Blade is a basic blade made with Slate, used for making Boards, Carving, and Slate Shovel.
A Slate Blade is created (Skills → Blades → Knap a Slate Blade) by striking two pieces of Slate together to create one sharpened piece; a process called Knapping.
Two pieces of Slate are required. When Knapping, one of two results are possible, creating a Slate Blade, or failure which consumes one or both pieces of Slate. Requires Knapping 0 (Skill), but as your Knapping skill improves, failures are less likely.
Farming, Skill/Filleting/0, Slate Scythe, Slate Shovel, Slate Shovel, Stone Knife, Technology/Farming/1