It’s actually marble, not alabaster or onyx. Beinecke Library interview
I didn’t get inside, but this building is supposed to warmly glow through the external marble walls.
“The thing about the Beinecke that’s interesting is the outside is cold and severe, and you walk inside and it’s very warm and rich. When the sun pours in, it’s quite nice with the rich books.” Gordon Bunshaft
Beinecke Rare Books Library, Yale, New Haven by Skidmore Owings Merrill