The 3rd mine has mystrile on all floors.
On Harvest Moon: DS and Harvest Moon: DS Cute, you get the third mine by reaching the bottom of the second mine, which is 255 floors deep.
You have to unlock the first mine by walking into the excavation site after 9pm. When you are in the first mine you must collect mystrile by breaking the rocks with your hammer. Make sure that you have the necessary levels for your tools by clicking on your asset screen and then the picture of yourself. If the levels are 100% call saibara the blacksmith and ask him to upgrade your tools to mystrile.
complete the first mine
On Harvest Moon DS (though I'm not sure which version you have) it is worth 40G.
3rd mine
In Harvest Moon DS and Cute, i believe you find the cursed tools in the deepest shaft of the mine.
To complete the mines in Harvest Moon DS cute you need to reach the bottom level of that Mine. These are the levels of the Mines 1st Mine: 10 floors 2cnd Mine: 255 3rd Mine: 999 floors 4th Mine: 65,535 Floors
255 floors
oh you mean the MYSTRILE? It's on the 8th floor. It's used for upgrading your tools. Hope i helped. :)
You have to get the Sword from the bottom of the second mine. After you reach the final floor defeat all the monsters and the large rock blocking your path into a room will open. You will not be able to pick the Sword up unless you have at least one of your tools upgraded to Mystrile level. In Harvest Moon DS Cute you'll need all of your tools upgraded to Mystrile. Take the Sword and use it on the large rock next to the waterfall. That will open the path to the Super Field.
Reach the bottom of the Third Mine. Then activate the Hammer Event with Carter again.
On Harvest Moon D.S. Cute you only have ONE.