So I was browsing ebay for any ending auctions, and saw this Indo-Greek coin, and wondered how it got this striations!
Would have to see it in hand and use a microscope but my first guess is differential corrosion due to a poorly mixed alloy. Over time the metal high in one element has leached out leaving areas low in that element. The coin has then been cleaned to give it an even overall finish. But that is only a guess. SC
Textile impressions in the patina from the cloth bag in which it had been buried is another possibility.
In all honesty, though, that coin looks more like a piece of raw, unrefined copper ore given its current condition.
Given the linear nature of the lines or grooves, on both sides, perhaps damaged, worn dies were used? There's also some corrosion present.
