From wow.incgamers.com

Talent Improvements

The Talents listed below affect Spellstone in the following mays.

Talent: Master Conjuror
Effect: Increases bonus fire damage from Firestones and the Firestone effect. Increases spell critical strike rating of Spellstone.
Statistics: 1 point = +15% fire dmg & crit rating, 2 points = +30%.

Facts about Spellstones

• Requires Soul Shard to conjur.
• Equipped in the ranged slot, therefore can use weapon and offhand slot at same time.
• The talent Master Conjuror increases the spell critical strike rating bonus by 15% with 1 point and 30% with 2.
• As a conjured item they will disappear if your character logs out or is disconnected for 15 minutes or more.