No the hardest mineral is Quartz because it's the most commonly used material after Titanium. However, unlike Titanium it is not infinite, so you can easily run out of it in your vacinity and will have to look for more in another biome.
Take the Alien Containment as example - you need 5 Glass which is 10 portions of Quartz and only 2 Titanium, however you need a Multipurpose Room for it which requires another 6 Titanium. But that's still more Quartz than Titanium that you need and that's just a single story tank, so if you build a multistory tank the demand for Quartz grows exponentially.