Cheapest priced copy (Double Masters 2022): $22.99 at Card Kingdom, near mint, their price list as of .
Thrumming Stone 
Legendary Artifact · Rare · The List · #CSP-142
Spells you cast have ripple 4. (Whenever you cast a spell, you may reveal the top four cards of your library. You may cast spells with the same name as that spell from among the revealed cards without paying their mana costs. Put the rest on the bottom of your library.)
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
4 printings · $22.99 to $69.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters 2022 | 315 | Rare | $22.99 | $27.99 |
| Double Masters 2022 | 567 | Rare | — | — |
| Coldsnap | 142 | Rare | $27.99 | $69.99 |
| The List | CSP-142 | Rare | $27.99 | — |
2 rulings from Wizards of the Coast
- 15 July 2006If you cast a spell that already has ripple (such as Surging Flame, which has ripple 4) while Thrumming Stone is on the battlefield, both ripple abilities will trigger separately. Assuming you choose to do all "you may" actions, when the first instance of ripple resolves, you reveal the top four cards of your library, cast all Surging Flames, and put the rest of the cards on the bottom of your library. Any new Surging Flames are on the stack on top of the other instance of ripple, so they'll resolve next. Each of them also has two instances of ripple, which trigger separately, and the process continues until the ripple abilities don't reveal any Surging Flames.
- 15 July 2006If you cast half of a split card (for example, Hit) and reveal another one of those split cards when the ripple ability resolves (for example, Hit // Run), you may cast either half of that split card (Hit or Run) without paying its mana cost.