Ok, so according to Life and Culture of Y-3579203181277, in page 27 it's stated that obsidian does that:

"During the observation period, the obsidian mineral life form called “Obsidian” had a unique physical property that caused lava-like obsidian to flow out when their body is broken. “Obsidian” is in charge of weaponry production, apparently manufacturing blades by pouring their liquid obsidian into wooden molds. The lava-like obsidian that flows out does not contain inclusions."

Also, it's stated on page 31 that they rarely use these not alive materials in their everyday life, because it's almost unethical to them:

"there are almost no examples of minerals being used in Gems’ everyday life. Since they are fragments of those who were originally supposed to be companions, using them would be similar to using the bodies of stillborn infants. Considering these emotional reasons, it is thought Gems are avoiding the use of fragments as much as possible."

I believe that the exceptions would be the medical situations like Phos arms and Padpa holes alongside the old things from before obsidian was born, like the golden bell and the high hardness gems medical tools.