Saw this article once about a guy who lost a date explaining how stars form. He said her eyes just went totally blank halfway through his bit about hydrogen fusion. Sometimes we get so into our own interests we forget most people just want to talk about normal stuff, like the music or the snacks. I mean, your garnet thing sounds cool, but maybe save it for like, a rock hounding group. It's all about reading the room, you know?
Ever catch yourself doing the glaze check mid-sentence? I was once three minutes into explaining my favorite video game's lore before I saw the soul leave their eyes.
What gets me is when people mistake someone being politely curious for a deep fascination. Like, you mention garnets and they say "oh neat," and suddenly you're explaining tectonic subduction zones while their eyes do that slow glaze-over thing. You're basically watching a person mentally queue up their grocery list. Save the mineral talk for when someone actually asks how old the rock is.