There are handful of divination spells that are blocked by barriers of a particular thickness and material, such as detect evil and good:
The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.
…and detect thoughts:
The spell can penetrate barriers, but 2 feet of rock, 2 inches of any metal other than lead, or a thin sheet of lead blocks you.
Would a wall of brick more than 2 feet thick block these spells (i.e. qualifying as stone or rock), or would that wall be a barrier that the spells can penetrate?
Best Answer
Technically, fired brick (the thing you think of as a brick, as opposed to mudbrick) is a form of ceramic, cooked in kilns; but I don't think there's much benefit in thinking about this too hard or getting overly technical about what a brick is on a microscopic physical level.
If you have to choose off the list of "dirt, wood, stone, or metal", stone seems the only appropriate option to use. If you're looking at a mudbrick wall, you might treat that as dirt, but that's kind of up to the DM to decide.