This is my offerin' rock. My blótstone. My elfmill.
Stones have been used as offering spaces for a long time, perhaps for as long as people have left offerings. Even the most mundane folks may surprise you, scattering bird seed on a large flat rock viewable from a window, just so that they could see the birds that come by to feast. Sacrifices to color on the wind.
Stones with dips in them, commonly called cup marked stones, oftentimes have concentric rings or animal figures carved around them. One of my favorite examples of this is Laxe Dos Cebros, which is known for its very distinctive stag figures (1p47) and many similar locations have a reputation for being associated with offerings.
Another term associated with these is elfmill, or elf-quern, derived from the term älvkvarnar, as, according to Ancestor Worship and the Elite in the Late Iron Sge Scandinavia, by Triin Laidoner, these markings were associated with Álfablót, a sacrifice to the álfar.
Of course, not all such structures were carved by human hands. Naturally occurring dips, or partial holes in stone can be caused by common environmental erosion, such as flowing water, or glaciers. These nature-made examples are also called älvkvarnar by some. (2p232)
Furthermore, according to Laidoner, Sweden not only has plenty of cup marks in stones, but they also appear on gravestones, indicating their use in offerings in ancestor worship.
Regardless, it's always nice to have something special with which to offer your gratitude. Just what makes something special is up to the individual, and while I'm sure many use bowls that are lovely, and equally effective, I do find that this stone is special as well.
1 Bradley, Richard. Rock Art and the Prehistory of Atlantic Europe: Signing the Land. Routledge, 2002.
2 Dodd, James, et al. Giving the Past a Future: Essays in Archaeology and Rock Art Studies in Honour of Dr. Phil. H.C. Gherhard Milstreu. Archaeopress Publishing Ltd, 2018.