Continuity mistake: On the spaceship, Peter is talking to Tony, and has his hair swept back with gel or similar. When he says "You can't be a friendly neighbourhood Spider-Man if there's no neighbourhood", we cut to Tony then back, and Peter now has a fringe with no gel. In later shots it's back how it was before.
Continuity mistake: When Heimdall is stabbed the sword gets into his chest around his heart, in the next scene they take the sword away from closer to his stomach.
Continuity mistake: When Thanos hits Wanda he is grabbing Vision by the neck, but in the next shot he grabs him again.
Continuity mistake: When Ebony Maw walks past the dead Asgardians, Corvus Glaive walks past him with his spear upright then the other way up. The spikes on the spear change shape too.
Continuity mistake: While Tony and Peter talk in Thanos' ship, Peter's hair changes between shots.
Continuity mistake: Before Heimdall sends Hulk to earth he moves his hand between shots.
Continuity mistake: When casting Thor's axe, the forge is barely tilted when the molten metal begins to pour, indicating it was almost full of material. But, in the previous shots, it is not, even after the bars melt.
Continuity mistake: While Iron Man talks with Thanos on Titan, Tony's facial hair changes color and amount.
Continuity mistake: Thanos stabs Heimdall in the chest but the spear is taken out from his stomach.
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