Finally washed some rocks

Sure. In basalts, lavas and other igneous rocks, gas vesicles often form as the material moves to the lower pressures near the surface. These voids later fill with fluid-borne minerals such as chalcedony, which preserve the bubbly or pebbly texture of the bubble in negative, and the result is an amygdule. This is the source of Great Lake agates, thomsonite, copper nuggets, etc. In some cases, these voids first are partially filled with calcite or zeolite formations before chalcedony fills the remainder; once freed from the basalt, the softer materials quickly dissolve or wear away, leaving their imprints in the harder chalcedony/agate.

Voids can also form in limestone seabed deposits and similarly get filled with chalcedony/agate/opal formations that preserve the shape of the void.

Fossil sponge is a great rarity - and almost never is actually sponge. The only hard parts of sponges that survive are the tiny (mostly microscopic), hard spicules. They look nothing like a sponge. The rest is fragile soft tissue that quickly dissolves away. The same reason that we know of ancient sharks almost entirely from their teeth and not their soft parts (the rest is soft tissue, skin and cartilage that doesn't survive).

Coral has a definite structure more akin to a honeycomb (thin, geometric walls forming short or long tubes, produced by the polyps) than a random bubble or pebble pattern. Compare to Petoskey Stone and other fossil and modern corals.

There is a similar pattern produced in softer stones by rock boring clams, but that isn't a fossil, usually only occurs on the exposed side of a stone, and is unlikely in harder rock.

Chalcedony and agate are quartz, and visible quartz crystals can grow in voids within them when the conditions are right.