Crystals are by definition ordered by a very regular pattern. I don't fully understand the mechanism, but I'm not surprised that it exists.

But glass isn't crystalline, it's amorphous, there's not really any order there on the atomic level.

Glass is not a crystal. Not sure what I was thinking. No idea why its surface is reflective.

Any abrupt change in refractive index, either higher or lower, will result in reflections. This can be somewhat intuited by analogy to sound waves, which reflect off of abrupt material density transitions.

This is how anti-reflective coatings work-- by "smoothing" the transition using materials that have intermediate refractive indices. E.g., flourite coatings on glass lenses.

I don't think people necessarily have an intuition about sound waves reflecting on material density transitions (the obvious one is air vs water but I guess unless you grew up near a lake or slow river you wouldn't know much about it), and I don't think it's clear how such an intuition - if present - would transfer from sound, which has a transmission medium, to light, which doesn't.

Sound is transmitted by waves of compression and decompression in the medium. In the reflection scenario that's is ultimately molecules of air and water hitting the boundary and transmitting some kinetic energy into the other medium and bouncing back, to some degree. You can visualize it as marbles hitting each other.

It's much harder to do the same for light.

If I think about the wave nature of light, then a material's refractive index is sort of the "density" of the medium. Light travels more slowly through materials with higher refractive index. As you know, this is actually due to the absorption and retransmission of photons from atom to atom, somewhat analogous to your marbles illustration of sound. Both models support wave-like behavior in aggregate.

Thus, when light moves from a "faster" medium to a "slower" one, refractions and reflections result that are similar in character to acoustic reflections.

That's how I think of it anyway.

I think that does make sense. A more extreme example is echos caused by sound bouncing off of solid materials. Definitely intuitive to me, unless someone can again explain why I am wrong. :)

That said, it explains why glass is shiny, but not necessarily why it is reflective. At least to my understanding.

not long ago I learned about metallic glass