Hello AlienEdge,
Any old rock? If you look at pictures they are going for a specific vein. They have been at this mine for at least 60+ years. They had a cave in some years ago, and had to dig it all out to access the vein again. It takes a hour and a half to reach the quarry, so that material is not used for making anything but sharpening stones.
Those prices are in pesos so 1500 is about 83 U.S. dollars, not very expensive at all for a 57 pound stone. If you look at the picture with the two stones from Monterey those two smaller ones sell for 1500 pesos plus shipping. The bigger white one is about 800-1200 grit and the black one is 4000-5000. While the one from Oaxaca is 4000-6000 and cut much faster than the black one. So it has a good reputation by the locals so that is why he never advertises them. They have a word of mouth reputation. The stone collector said it was his favorite because it cut faster and was finer, not to mention much bigger and at a much lower price.
The seller has a regular job and sells stones on the weekends that is how my cousin found him. At a market stalls that only set up on the off days. So he works seven days a week. Every time we talk he usualy has to do something and then calls me back at a latter time. He said that the miner is his uncle by marriage and that is how he got into selling the stones.
Making a road to the quarry that takes a hour and a half to reach by foot up a mountain would be very expensive so that is out of the question. He stated when it rained it was not accessible to reach by foot so that tells me it is a steep road. I googled the area and they put the alevation from 1500m to 2500m. So that puts this mine at over a mile high.
I have many stones from around the world, I try to buy the best I can afford and have a good idea what to look for in a stone. I always wanted a sharpening stone from Mexico as it reminds me of my grandfather who sharpened his own knives, that got me first interested on this hobby. It reminds me of him and he was a great man that brings me closer to him.
I was very happy when I found this stone and just sharing my expirience. That is all.
Good day to all,
Israel