On a single dirt tile with gold you can see gold on every side of the tile. But if the tile is next to another dirt there is gold only on 2 sides.
Other diggable tiles should be checked too.
For review by Cian in 2018.
Found a moment to give this a test. Confirmed this behaviour with Earth tiles and Brimstone. Suspect it affects all tile types.
See attached screenshot as demonstration:
Intended. To provide a little bit of variation
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