I'm Pre-Hardmode, Expert Large World, with an Iron Pickaxe, and Underground.  I spotted some sort of shiny rock in the dark, dug my way to it, and found that I can't seem to break it.  I hit it, and its image changes, but no breaking.  I looked up what materials need high levels of pickaxes to break them, but it doesn't seem to fit any of them, since it seems none of them should be Underground, Pre-Hardmode?  I haven't seen any lava yet, either.  No Screenshot, right now.
I just came across this glowy ore, and my 'Sharp Silver Pickaxe' won't mine it. I'm playing on the PC version of Terraria, if that helps.  How do I mine the glowy ore block?
I've noticed an interesting phenomenon in the user interfaces of many famous applications, they're moving away from the glossy complex to a more dull and bare minimum design.  Why the sudden change? It also appears that most of these companies have adopted this design around the same time, was that linked to some new study?  Examples: