Can you scratch shale with your fingernails?

No, you generally cannot scratch shale with your fingernails. Shale is a sedimentary rock that is relatively hard and composed of clay minerals, making it more resistant to scratching. Fingernails have a hardness of about 2.5 on the Mohs scale, while shale typically has a hardness of around 3 to 4. Therefore, a fingernail would not be able to leave a scratch on shale.