Public domain photos

The image shows a close up of a piece of rock with a ruler next to it, and at the top of the image there is some text. The rock appears to be a sponge, with a light brown color and a rough texture. The ruler is a standard measuring scale with a black background.

The image shows a close up of a piece of rock with a ruler next to it, and at the top of the image there is some text. The rock appears to be a sponge, with a light brown color and a rough texture. The ruler is a standard measuring scale with a black background.Open in library