T'Challa: Today we don't fight for any life... we fight for ALL of them.
Natasha Romanoff: Where's your other friend?
Proxima Midnight: He will pay for his life with yours. Thanos will have that stone.
Steve Rogers: That's not gonna happen.
T'Challa: You are in Wakanda now. Thanos will have nothing but dust, and blood.
Proxima Midnight: We have blood to spare.
Tony Stark: Are you yawning?
[Drax yawns.]
Tony Stark: In the middle of this, while I'm breaking it down? Huh? Did you hear what I said?
Drax: I stopped listening after you said "We need a plan."
Tony Stark: Okay, Mr. Clean is on his own page.
Drax: Die, blanket of death.
[Cull Obsidian attempts to kill Tony, but Wong opens a portal sending him to a snowy location, closes the portal, severing his hand and trapping him there.]
Tony Stark: Wong, you're invited to my wedding.
[Bruce attempts to turn into the Hulk, but fails.]
Tony Stark: Dude, you're embarrassing me in front of the wizards.
Ebony Maw: Hear me and rejoice. You have had the privilege of being saved by the Great Titan. You may think this is suffering. No. It is salvation. Universal scales tip towards balance because of your sacrifice. Smile. For even in death, you have become children of Thanos.
Thor: You know, I'm 1500 years old. I've killed twice as many enemies as that. And every one of them would have rather killed me than not succeeded. I'm only alive because fate wants me alive. Thanos is just the latest of a long line of bastards, and he'll be the latest to feel my vengeance - fate wills it so.
Thanos: When I'm done, half of humanity will still exist. Perfectly balanced, as all things should be... I hope they remember you.
Gamora: The entire time I knew him, he only ever had one goal. To wipe out half the universe. If he gets all the Infinity Stones, he can do it with the snap of his fingers. Just like that.
Thor: Something is very wrong.
T'Challa: Evacuate the city! Engage all defenses! And get this man a shield!
Thanos: With all the six stones I can simply snap my fingers, they will all cease to exist. I call that mercy.
Dr. Stephen Strange: Then what?
Thanos: Finally rest. Watch the sun rise on an ungrateful universe. The hardest choices require the strongest will.
Rocket: Ooh, I would have washed that if I were you. The only way to sneak it off Contraxia was up my a...
Eitri: You're about to take the full power of a star. It will kill you.
Thor: Only if I die.
Dr. Strange: He could destroy life on a scale hitherto undreamt of.
Tony Stark: Did you seriously just say hitherto undreamt of?
Dr. Strange: Are you seriously leaning on the Cauldron of the Cosmos?
Tony Stark: Is that what it is? [Gets hit by the cloak of levitation] I'm going to allow that. If Thanos needs all six why don't we just stick this one down a garbage disposal?
Dr. Strange: No can do.
Stark: What is your job exactly besides making balloon animals?
Strange Protecting your reality, douchebag.
Wong: A hunk of Hulk of Burning Fudge is our favorite.
Banner: That's a thing?
Stark: Whatever.
Answer: "Doctor Strange" demonstrates that the Infinity Stones are useful in the most dire of situations, when Strange used the Time Stone to prevent Dormammu from taking over the Earth. It's also possible that some of the stones are indestructible. Wanda is able to temporarily destroy the Mind Stone by using her own powers, but the Power Stone will destroy any being that doesn't possess the strength to wield it, and the Reality Stone is shown to have a will of its own and defended itself when it bonded with Jane Foster.
Phaneron ★
Also, in the comics, if the stones are destroyed they will simply be replaced by something else or even stones again. They represent the existence of the universe and cannot be destroyed for real. Always only temporarily.
lionhead