There is a legend or possibly Midrash that states the rocks of Mount Sinai were imprinted with an image of a bush to commemorate Moses' encounter with the burning bush.
I once heard an explanation in the name of a Midrash: "When G-d sent Moses to Egypt to report to the Jews about the redemption and then to come back to Mount Sinai, Moses asked G-d: 'how will I be sure which mountain to return to?' (since at first, G-d spoke to Moses only from Mount Sinai). G-d made a miracle and all the rocks from Mount Sinai became engraved with the 'burning bush'".
Now, we cannot be 100 percent sure where Mount Sinai is, but there is such a mountain in the Sinai peninsula where all its rocks have fern-like patterns on its sides. Local Bedouins maintain no such autograph appears in any other mountain in the Sinai peninsula.
I have personally seen stones from there and they indeed have this pattern. Some want to "debunk" this Midrash by saying such a phenomena exists elsewhere, i.e. although it is rare, there exists similar patterns on the surface of rocks elsewhere in the world, such as in India and California. The phenomena is called "crystal dendrites".
However, just because it exists elsewhere does not mean the Midrash is not correct. Perhaps G-d chose a natural phenomena to occur at that particular place. As is known, G-d runs the world in such a way that miracles are minimized.
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