Up for sale is the mana-storing Basalt Monolith, an uncommon card from the Unlimited (2nd) Edition of Magic: the Gathering. This is the original, white-bordered, English version.
Basalt Monolith: Artifact; Basalt Monolith doesn't untap during your untap step; spend 3 mana to untap Basalt Monolith; tap Basalt Monolith to add 3 mana to your mana pool; casting cost 3.
These cards are all in at least Very Fine condition, with most being in unplayed, Mint/Near Mint condition.