Slate is a rock, so you won't find it listed on the Mohs Scale, because that scale of hardness applies to minerals. I'll go out on a limb though, and suggest that slate is probably around 2 to 3 or so, but this will be variable, depending on the quality of the slate, and degree of weathering, etc.
Limonite has a hardness of about 4 to 5.5 on the Mohs hardness scale.
A fingernail has a hardness of around 2.5 on the Mohs hardness scale, which means it can be easily scratched by materials with a higher hardness level.
The fourth mineral on Mohs' Scale of Hardness is fluorite. It has a hardness of 4 on the scale.
The Mohs Scale of Hardness determines the hardness of minerals by scratching them with commonly found objects. The minerals are assigned a number which corresponds to their hardness; higher numbers indicate higher hardness.
The hardness is 6 on the MOHS scale
Slate has a hardness of around 5.5 on the Mohs hardness scale, which means it is relatively soft and can be easily scratched by harder materials.
Diatomite has a hardness of around 5.5 on the Mohs scale of hardness.
The mineral hardness scale is called the Mohs scale of mineral hardness, named after German geologist Friedrich Mohs who created it in 1812.
Limonite has a hardness of about 4 to 5.5 on the Mohs hardness scale.
Azurite has a hardness of 3.5 to 4 on the Mohs hardness scale.
Flint has a hardness of 7 on the Mohs scale of hardness.
Nickel has a hardness of 4 on the Mohs scale.
The hardness is 3-4 on Mohs scale.
Dolomite has a hardness of 3.5 to 4 on the Mohs hardness scale.
The Mohs scale is used to determine the relative hardness of minerals.
Friedrich Mohs' hardness scale is simply known as the Mohs Scale of Mineral Hardness.
Aluminum Oxide is roughly 8.5 - 9.0 on the hardness scale.