Detail this asset from Unity Store: Original Link
This is a paid asset, but now you can download Hand Painted Texture Pack – Natural Surfaces Free.
Hand Painted Texture Pack – Natural Surfaces v1.10
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This pack contains 133 highly detailed textures depicting all kinds of surfaces commonly found in natural environments. Contents: 24 Ground textures, 10 Mud textures, 8 Volcanic textures, 36 Rock textures, 19 Forest textures, 19 Grass textures, 13 Sand textures and 4 Winter textures.
All pictures come in 512×512 resolution and are fully tileable.
The set is being updated occasionally with new textures as well as new variations for existing ones.