Gathering Stone
As this artifact enters, choose a creature type.
Spells you cast of the chosen type cost 
less to cast.
When this artifact enters and at the beginning of your upkeep, look at the top card of your library. If it's a card of the chosen type, you may reveal it and put it into your hand. If you don't put the card into your hand, you may put it into your graveyard.
Illustrated by Paolo Parente
This printing
Prices
To determine the total cost of a spell, start with the mana cost or alternative cost you're paying (such as a flashback cost), add any cost increases (such as kicker costs), then apply any cost reductions (such as that of this ability). The mana value of the spell is determined by only its mana cost, no matter what the total cost to cast that spell was.
You don't have to reveal the card you look at with Gathering Stone's third ability even if it's a card of the chosen type. If you choose not to reveal it this way, you can still put it into your graveyard.
Gathering Stone's second ability applies only to generic mana in the total cost of spells you cast of the chosen type.
