I was on a beach recently and was contemplating what it would look like if Silicon just didn't bind oxygen very well/at all, perhaps similar to gold.
I'm not sure if something else would take the oxygen's place and create a similar environment to a beach, since silicon is very similar to carbon on the periodic table (Perhaps hydrogen due to its abundance?).
Silicon is also the second most abundant element in Earth's crust and has a high affinity for oxygen.
There need not be any fundamental shift in how chemistry works, perhaps an AI from the first civilization to ever exist in the universe just makes this so by subtly changing physical rules (To the extent such a thing actually exists) in the area in the are to preserve how chemistry normally operated, just minus this one exception.
What exactly would a beach look like since it is mostly composed of SiO_2? Would beaches be more metallic in appearance? Would beaches remain mostly the same, but just with silicon bonded to other elements instead of oxygen?