Hi, good question. I cant confirm but I think they dont have a quartz mine yet where they can mine, they have applied for a license of quartz mine, its under process. Currently they source the qurtz from a supplier mine close to Vizag.
And PESL is like a factory, not a mining subsidiary as you think , it processes natural quartz material into a manufactured stone. Please read more about how Quartz stone is made.
And the company is 2-3 decades old, I believe they have acquired and developed granite mines over the years, but I think its good to ask them.
Thanks-Mahesh